Michael P. Minitti

All Publications

• Brighter, faster, stronger: ultrafast scattering of free molecules ADVANCES IN PHYSICS-X Odate, A., Kirrander, A., Weber, P. M., Minitti, M. P. 2023; 8 (1)

  View details for DOI 10.1080/23746149.2022.2126796

  View details for Web of Science ID 000905603600001

• Transient vibration and product formation of photoexcited CS2 measured by time-resolved x-ray scattering. The Journal of chemical physics Gabalski, I., Sere, M., Acheson, K., Allum, F., Boutet, S., Dixit, G., Forbes, R., Glownia, J. M., Goff, N., Hegazy, K., Howard, A. J., Liang, M., Minitti, M. P., Minns, R. S., Natan, A., Peard, N., Rasmus, W. O., Sension, R. J., Ware, M. R., Weber, P. M., Werby, N., Wolf, T. J., Kirrander, A., Bucksbaum, P. H. 2022; 157 (16): 164305

  Abstract

  We have observed details of the internal motion and dissociation channels in photoexcited carbon disulfide (CS2) using time-resolved x-ray scattering (TRXS). Photoexcitation of gas-phase CS2 with a 200nm laser pulse launches oscillatory bending and stretching motion, leading to dissociation of atomic sulfur in under a picosecond. During the first 300fs following excitation, we observe significant changes in the vibrational frequency as well as some dissociation of the C-S bond, leading to atomic sulfur in the both 1D and 3P states. Beyond 1400fs, the dissociation is consistent with primarily 3P atomic sulfur dissociation. This channel-resolved measurement of the dissociation time is based on our analysis of the time-windowed dissociation radial velocity distribution, which is measured using the temporal Fourier transform of the TRXS data aided by a Hough transform that extracts the slopes of linear features in an image. The relative strength of the two dissociation channels reflects both their branching ratio and differences in the spread of their dissociation times. Measuring the time-resolved dissociation radial velocity distribution aids the resolution of discrepancies between models for dissociation proposed by prior photoelectron spectroscopy work.

  View details for DOI 10.1063/5.0113079

  View details for PubMedID 36319419

• Following Metal-to-Ligand Charge-Transfer Dynamics with Ligand and Spin Specificity Using Femtosecond Resonant Inelastic X-ray Scattering at the Nitrogen K-Edge. The journal of physical chemistry letters Jay, R. M., Eckert, S., Van Kuiken, B. E., Ochmann, M., Hantschmann, M., Cordones, A. A., Cho, H., Hong, K., Ma, R., Lee, J. H., Dakovski, G. L., Turner, J. J., Minitti, M. P., Quevedo, W., Pietzsch, A., Beye, M., Kim, T. K., Schoenlein, R. W., Wernet, P., Fohlisch, A., Huse, N. 2021: 6676-6683

  Abstract

  We demonstrate for the case of photoexcited [Ru(2,2'-bipyridine)3]2+ how femtosecond resonant inelastic X-ray scattering (RIXS) at the ligand K-edge allows one to uniquely probe changes in the valence electronic structure following a metal-to-ligand charge-transfer (MLCT) excitation. Metal-ligand hybridization is probed by nitrogen-1s resonances providing information on both the electron-accepting ligand in the MLCT state and the hole density of the metal center. By comparing to spectrum calculations based on density functional theory, we are able to distinguish the electronic structure of the electron-accepting ligand and the other ligands and determine a temporal upper limit of (250 ± 40) fs for electron localization following the charge-transfer excitation. The spin of the localized electron is deduced from the selection rules of the RIXS process establishing new experimental capabilities for probing transient charge and spin densities.

  View details for DOI 10.1021/acs.jpclett.1c01401

  View details for PubMedID 34260255

• Determination of excited state molecular structures from time-resolved gas-phase X-ray scattering. Faraday discussions Yong, H., Moreno Carrascosa, A., Ma, L., Stankus, B., Minitti, M. P., Kirrander, A., Weber, P. M. 2021

  Abstract

  We present a comprehensive investigation of a recently introduced method to determine transient structures of molecules in excited electronic states with sub-angstrom resolution from time-resolved gas-phase scattering signals. The method, which is examined using time-resolved X-ray scattering data measured on the molecule N-methylmorpholine (NMM) at the Linac Coherent Light Source (LCLS), compares the experimentally measured scattering patterns against the simulated patterns corresponding to a large pool of molecular structures to determine the full set of structural parameters. In addition, we examine the influence of vibrational state distributions and find the effect negligible within the current experimental detection limits, despite that the molecules have a comparatively high internal vibrational energy. The excited state structures determined using three structure pools generated using three different computational methods are in good agreement, demonstrating that the procedure is largely independent of the computational chemistry method employed as long as the pool is sufficiently expansive in the vicinity of the sought structure and dense enough to yield good matches to the experimental patterns.

  View details for DOI 10.1039/d0fd00118j

  View details for PubMedID 33595043

• Electron-ion coincidence measurements of molecular dynamics with intense X-ray pulses. Scientific reports Li, X., Inhester, L., Osipov, T., Boll, R., Coffee, R., Cryan, J., Gatton, A., Gorkhover, T., Hartman, G., Ilchen, M., Knie, A., Lin, M., Minitti, M. P., Weninger, C., Wolf, T. J., Son, S., Santra, R., Rolles, D., Rudenko, A., Walter, P. 2021; 11 (1): 505

  Abstract

  Molecules can sequentially absorb multiple photons when irradiated by an intense X-ray pulse from a free-electron laser. If the time delay between two photoabsorption events can be determined, this enables pump-probe experiments with a single X-ray pulse, where the absorption of the first photon induces electronic and nuclear dynamics that are probed by the absorption of the second photon. Here we show a realization of such a single-pulse X-ray pump-probe scheme on N[Formula: see text] molecules, using the X-ray induced dissociation process as an internal clock that is read out via coincident detection of photoelectrons and fragment ions. By coincidence analysis of the kinetic energies of the ionic fragments and photoelectrons, the transition from a bound molecular dication to two isolated atomic ions is observed through the energy shift of the inner-shell electrons. Via ab-initio simulations, we are able to map characteristic features in the kinetic energy release and photoelectron spectrum to specific delay times between photoabsorptions. In contrast to previous studies where nuclear motions were typically revealed by measuring ion kinetics, our work shows that inner-shell photoelectron energies can also be sensitive probes of nuclear dynamics, which adds one more dimension to the study of light-matter interactions with X-ray pulses.

  View details for DOI 10.1038/s41598-020-79818-6

  View details for PubMedID 33436816

• Ultrafast X-ray scattering offers a structural view of excited-state charge transfer. Proceedings of the National Academy of Sciences of the United States of America Yong, H. n., Xu, X. n., Ruddock, J. M., Stankus, B. n., Carrascosa, A. M., Zotev, N. n., Bellshaw, D. n., Du, W. n., Goff, N. n., Chang, Y. n., Boutet, S. n., Carbajo, S. n., Koglin, J. E., Liang, M. n., Robinson, J. S., Kirrander, A. n., Minitti, M. P., Weber, P. M. 2021; 118 (19)

  Abstract

  Intramolecular charge transfer and the associated changes in molecular structure in N,N'-dimethylpiperazine are tracked using femtosecond gas-phase X-ray scattering. The molecules are optically excited to the 3p state at 200 nm. Following rapid relaxation to the 3s state, distinct charge-localized and charge-delocalized species related by charge transfer are observed. The experiment determines the molecular structure of the two species, with the redistribution of electron density accounted for by a scattering correction factor. The initially dominant charge-localized state has a weakened carbon-carbon bond and reorients one methyl group compared with the ground state. Subsequent charge transfer to the charge-delocalized state elongates the carbon-carbon bond further, creating an extended 1.634 Å bond, and also reorients the second methyl group. At the same time, the bond lengths between the nitrogen and the ring-carbon atoms contract from an average of 1.505 to 1.465 Å. The experiment determines the overall charge transfer time constant for approaching the equilibrium between charge-localized and charge-delocalized species to 3.0 ps.

  View details for DOI 10.1073/pnas.2021714118

  View details for PubMedID 33947814

• Advances in ultrafast gas-phase x-ray scattering JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS Stankus, B., Yong, H., Ruddock, J., Ma, L., Carrascosa, A., Goff, N., Boutet, S., Xu, X., Zotev, N., Kirrander, A., Minitti, M. P., Weber, P. M. 2020; 53 (23)

  View details for DOI 10.1088/1361-6455/abbfea

  View details for Web of Science ID 000588835200001

• High-sensitivity x-ray/optical cross-correlator for next generation free-electron lasers OPTICS EXPRESS Droste, S., Zohar, S., Shen, L., White, V. E., Diaz-Jacobo, E., Coffee, R. N., Reid, A. H., Tavella, F., Minitti, M. P., Turner, J. J., Robinson, J. S., Fry, A. R., Coslovich, G. 2020; 28 (16): 23545–53

  Abstract

  We design and realize an arrival time diagnostic for ultrashort X-ray pulses achieving unprecedented high sensitivity in the soft X-ray regime via cross-correlation with a ≈1550 nm optical laser. An interferometric detection scheme is combined with a multi-layer sample design to greatly improve the sensitivity of the measurement. We achieve up to 275% of relative signal change when exposed to 1.6 mJ/cm2 of soft X-rays at 530 eV, more than a hundred-fold improvement in sensitivity as compared to previously reported techniques. The resolution of the arrival time measurement is estimated to around 2.8 fs (rms). The demonstrated X-ray arrival time monitor paves the way for sub-10 fs-level timing jitter at high repetition rate X-ray facilities.

  View details for DOI 10.1364/OE.398048

  View details for Web of Science ID 000560931200042

  View details for PubMedID 32752349

• Observation of the molecular response to light upon photoexcitation. Nature communications Yong, H., Zotev, N., Ruddock, J. M., Stankus, B., Simmermacher, M., Carrascosa, A. M., Du, W., Goff, N., Chang, Y., Bellshaw, D., Liang, M., Carbajo, S., Koglin, J. E., Robinson, J. S., Boutet, S., Minitti, M. P., Kirrander, A., Weber, P. M. 2020; 11 (1): 2157

  Abstract

  When a molecule interacts with light, its electrons can absorb energy from the electromagnetic field by rapidly rearranging their positions. This constitutes the first step of photochemical and photophysical processes that include primary events in human vision and photosynthesis. Here, we report the direct measurement of the initial redistribution of electron density when the molecule 1,3-cyclohexadiene (CHD) is optically excited. Our experiments exploit the intense, ultrashort hard x-ray pulses of the Linac Coherent Light Source (LCLS) to map the change in electron density using ultrafast x-ray scattering. The nature of the excited electronic state is identified with excellent spatial resolution and in good agreement with theoretical predictions. The excited state electron density distributions are thus amenable to direct experimental observation.

  View details for DOI 10.1038/s41467-020-15680-4

  View details for PubMedID 32358535

• Ultrafast X-ray scattering reveals vibrational coherence following Rydberg excitation. Nature chemistry Stankus, B., Yong, H., Zotev, N., Ruddock, J. M., Bellshaw, D., Lane, T. J., Liang, M., Boutet, S., Carbajo, S., Robinson, J. S., Du, W., Goff, N., Chang, Y., Koglin, J. E., Minitti, M. P., Kirrander, A., Weber, P. M. 2019

  Abstract

  The coherence and dephasing of vibrational motions of molecules constitute an integral part of chemical dynamics, influence material properties and underpin schemes to control chemical reactions. Considerable progress has been made in understanding vibrational coherence through spectroscopic measurements, but precise, direct measurement of the structure of a vibrating excited-state polyatomic organic molecule has remained unworkable. Here, we measure the time-evolving molecular structure of optically excited N-methylmorpholine through scattering with ultrashort X-ray pulses. The scattering signals are corrected for the differences in electron density in the excited electronic state of the molecule in comparison to the ground state. The experiment maps the evolution of the molecular geometry with femtosecond resolution, showing coherent motion that survives electronic relaxation and seems to persist for longer than previously seen using other methods.

  View details for DOI 10.1038/s41557-019-0291-0

  View details for PubMedID 31285542

• Simplicity beneath Complexity: Counting Molecular Electrons Reveals Transients and Kinetics of Photodissociation Reactions. Angewandte Chemie (International ed. in English) Ruddock, J. M., Zotev, N., Stankus, B., Yong, H., Bellshaw, D., Boutet, S., Lane, T. J., Liang, M., Carbajo, S., Du, W., Kirrander, A., Minitti, M. P., Weber, P. M. 2019

  Abstract

  Time-resolved pump-probe gas phase X-ray scattering signals, extrapolated to zero momentum transfer, provide a measure of the number of electrons in a system, an effect that arises from the coherent addition of elastic scattering from the electrons. This allows for the identification of reactive transients and the determination of the chemical reaction kinetics without the need for extensive scattering simulations or complicated inversion of scattering data. We examine the photodissociation reaction of trimethyl amine, and identify two reaction paths upon excitation to the 3p state at 200 nm: a fast dissociation path out of the 3p state to the dimethyl amine radical (16.6±1.2%), and a slower dissociation via internal conversion to the 3s state (83.4±1.2%). The time constants for the two reactions are 640±130 fs and 74±6 ps, respectively. In addition, it is found that the transient dimethyl amine radical has a N-C bond length of 1.45±0.02 A and a CNC bond angle of 118°±4°.

  View details for PubMedID 30866169

• Soft X-ray spectroscopy with transition-edge sensors at Stanford Synchrotron Radiation Lightsource beamline 10-1. The Review of scientific instruments Lee, S. J., Titus, C. J., Alonso Mori, R. n., Baker, M. L., Bennett, D. A., Cho, H. M., Doriese, W. B., Fowler, J. W., Gaffney, K. J., Gallo, A. n., Gard, J. D., Hilton, G. C., Jang, H. n., Joe, Y. I., Kenney, C. J., Knight, J. n., Kroll, T. n., Lee, J. S., Li, D. n., Lu, D. n., Marks, R. n., Minitti, M. P., Morgan, K. M., Ogasawara, H. n., O'Neil, G. C., Reintsema, C. D., Schmidt, D. R., Sokaras, D. n., Ullom, J. N., Weng, T. C., Williams, C. n., Young, B. A., Swetz, D. S., Irwin, K. D., Nordlund, D. n. 2019; 90 (11): 113101

  Abstract

  We present results obtained with a new soft X-ray spectrometer based on transition-edge sensors (TESs) composed of Mo/Cu bilayers coupled to bismuth absorbers. This spectrometer simultaneously provides excellent energy resolution, high detection efficiency, and broadband spectral coverage. The new spectrometer is optimized for incident X-ray energies below 2 keV. Each pixel serves as both a highly sensitive calorimeter and an X-ray absorber with near unity quantum efficiency. We have commissioned this 240-pixel TES spectrometer at the Stanford Synchrotron Radiation Lightsource beamline 10-1 (BL 10-1) and used it to probe the local electronic structure of sample materials with unprecedented sensitivity in the soft X-ray regime. As mounted, the TES spectrometer has a maximum detection solid angle of 2 × 10-3 sr. The energy resolution of all pixels combined is 1.5 eV full width at half maximum at 500 eV. We describe the performance of the TES spectrometer in terms of its energy resolution and count-rate capability and demonstrate its utility as a high throughput detector for synchrotron-based X-ray spectroscopy. Results from initial X-ray emission spectroscopy and resonant inelastic X-ray scattering experiments obtained with the spectrometer are presented.

  View details for DOI 10.1063/1.5119155

  View details for PubMedID 31779391

• A deep UV trigger for ground-state ring-opening dynamics of 1,3-cyclohexadiene. Science advances Ruddock, J. M., Yong, H. n., Stankus, B. n., Du, W. n., Goff, N. n., Chang, Y. n., Odate, A. n., Carrascosa, A. M., Bellshaw, D. n., Zotev, N. n., Liang, M. n., Carbajo, S. n., Koglin, J. n., Robinson, J. S., Boutet, S. n., Kirrander, A. n., Minitti, M. P., Weber, P. M. 2019; 5 (9): eaax6625

  Abstract

  We explore the photo-induced kinetics of 1,3-cyclohexadiene upon excitation at 200 nm to the 3p state by ultrafast time-resolved, gas-phase x-ray scattering using the Linac Coherent Light Source. Analysis of the scattering anisotropy reveals that the excitation leads to the 3px and 3py Rydberg electronic states, which relax to the ground state with a time constant of 208 ± 11 fs. In contrast to the well-studied 266 nm excitation, at 200 nm the majority of the molecules (76 ± 3%) relax to vibrationally hot cyclohexadiene in the ground electronic state. A subsequent reaction on the ground electronic state surface leads from the hot cyclohexadiene to 1,3,5-hexatriene, with rates for the forward and backward reactions of 174 ± 13 and 355 ± 45 ps, respectively. The scattering pattern of the final hexatriene product reveals a thermal distribution of rotamers about the carbon-carbon single bonds.

  View details for DOI 10.1126/sciadv.aax6625

  View details for PubMedID 31523713

  View details for PubMedCentralID PMC6731073

• Scattering off molecules far from equilibrium. The Journal of chemical physics Yong, H. n., Ruddock, J. M., Stankus, B. n., Ma, L. n., Du, W. n., Goff, N. n., Chang, Y. n., Zotev, N. n., Bellshaw, D. n., Boutet, S. n., Carbajo, S. n., Koglin, J. E., Liang, M. n., Robinson, J. S., Kirrander, A. n., Minitti, M. P., Weber, P. M. 2019; 151 (8): 084301

  Abstract

  Pump-probe gas phase X-ray scattering experiments, enabled by the development of X-ray free electron lasers, have advanced to reveal scattering patterns of molecules far from their equilibrium geometry. While dynamic displacements reflecting the motion of wavepackets can probe deeply into the reaction dynamics, in many systems, the thermal excitation embedded in the molecules upon optical excitation and energy randomization can create systems that encompass structures far from the ground state geometry. For polyatomic molecular systems, large amplitude vibrational motions are associated with anharmonicity and shifts of interatomic distances, making analytical solutions using traditional harmonic approximations inapplicable. More generally, the interatomic distances in a polyatomic molecule are not independent and the traditional equations commonly used to interpret the data may give unphysical results. Here, we introduce a novel method based on molecular dynamic trajectories and illustrate it on two examples of hot, vibrating molecules at thermal equilibrium. When excited at 200 nm, 1,3-cyclohexadiene (CHD) relaxes on a subpicosecond time scale back to the reactant molecule, the dominant pathway, and to various forms of 1,3,5-hexatriene (HT). With internal energies of about 6 eV, the energy thermalizes quickly, leading to structure distributions that deviate significantly from their vibrationless equilibrium. The experimental and theoretical results are in excellent agreement and reveal that a significant contribution to the scattering signal arises from transition state structures near the inversion barrier of CHD. In HT, our analysis clarifies that previous inconsistent structural parameters determined by electron diffraction were artifacts that might have resulted from the use of inapplicable analytical equations.

  View details for DOI 10.1063/1.5111979

  View details for PubMedID 31470697

• Imaging the ring opening reaction of 1,3-cyclohexadiene with MeV ultrafast electron diffraction Wolf, T. A., Yang, J., Sanchez, D. M., Nunes, J. F., Parrish, R. M., Shen, X., Centurion, M., Coffee, R., Gyan, J. P., Guhr, M., Kareem, H., Kirrander, A., Li, R., Ruddock, J., Veccione, T., Weathersby, S. P., Weber, P. M., Wilkin, K., Yong, H., Zheng, Q., Martinez, T. J., Wang, X., Minitti, M. P., Cerullo, G., Ogilvie, J., Kartner, F., Khalil, M., Li, R. E D P SCIENCES. 2019

  View details for DOI 10.1051/epjconf/201920507006

  View details for Web of Science ID 000570451400143

• The photochemical ring-opening of 1,3-cyclohexadiene imaged by ultrafast electron diffraction. Nature chemistry Wolf, T. J., Sanchez, D. M., Yang, J. n., Parrish, R. M., Nunes, J. P., Centurion, M. n., Coffee, R. n., Cryan, J. P., Gühr, M. n., Hegazy, K. n., Kirrander, A. n., Li, R. K., Ruddock, J. n., Shen, X. n., Vecchione, T. n., Weathersby, S. P., Weber, P. M., Wilkin, K. n., Yong, H. n., Zheng, Q. n., Wang, X. J., Minitti, M. P., Martínez, T. J. 2019

  Abstract

  The ultrafast photoinduced ring-opening of 1,3-cyclohexadiene constitutes a textbook example of electrocyclic reactions in organic chemistry and a model for photobiological reactions in vitamin D synthesis. Although the relaxation from the photoexcited electronic state during the ring-opening has been investigated in numerous studies, the accompanying changes in atomic distance have not been resolved. Here we present a direct and unambiguous observation of the ring-opening reaction path on the femtosecond timescale and subångström length scale using megaelectronvolt ultrafast electron diffraction. We followed the carbon-carbon bond dissociation and the structural opening of the 1,3-cyclohexadiene ring by the direct measurement of time-dependent changes in the distribution of interatomic distances. We observed a substantial acceleration of the ring-opening motion after internal conversion to the ground state due to a steepening of the electronic potential gradient towards the product minima. The ring-opening motion transforms into rotation of the terminal ethylene groups in the photoproduct 1,3,5-hexatriene on the subpicosecond timescale.

  View details for PubMedID 30988415

• Determining Orientations of Optical Transition Dipole Moments Using Ultrafast X-ray Scattering JOURNAL OF PHYSICAL CHEMISTRY LETTERS Yong, H., Zotev, N., Stankus, B., Ruddock, J. M., Bellshaw, D., Boutet, S., Lane, T. J., Liang, M., Carbajo, S., Robinson, J. S., Du, W., Goff, N., Chang, Y., Koglin, J. E., Waters, M. J., Solling, T. I., Minitti, M. P., Kirrander, A., Weber, P. M. 2018; 9 (22): 6556–62

  View details for DOI 10.1021/acs.jpclett.8b02773

  View details for Web of Science ID 000451362100027

• Self-consistent internal calibration of x-ray scattering patterns from polarized radiation sources Goff, N., Stankus, B., Ruddock, J., Zhang, Y., Lane, T., Liang, M., Boutet, S., Carbajo, S., Robinson, J., Koglin, J., Aquila, A., Minitti, M., Weber, P. AMER CHEMICAL SOC. 2018

  View details for Web of Science ID 000447609104035

• Deconvoluting the isotropic and anisotropic ultrafast x-ray scattering of gas-phase N-methylmorpholine following Rydberg excitation Stankus, B., Ruddock, J., Yong, H., Zotev, N., Bellshaw, D., Lane, T., Boutet, S., Liang, M., Carbajo, S., Robinson, J., Koglin, J., Aquila, A., Zhang, Y., Du, W., Goff, N., Chang, Y., Minitti, M., Kirrander, A., Weber, P. AMER CHEMICAL SOC. 2018

  View details for Web of Science ID 000447609103461

• Exploring molecular reaction dynamics by ultrafast time-resolved gas phase X-ray scattering Minitti, M., Ruddock, J., Stankus, B., Du, W., Yong, H., Goff, N., Bellshaw, D., Zotev, N., Liang, M., Boutet, S., Kirrander, A., Weber, P. AMER CHEMICAL SOC. 2018

  View details for Web of Science ID 000447609103781

• Time-resolved gas-phase X-ray scattering to reveal transients in photodissociation reactions Ruddock, J., Stankus, B., Yong, H., Du, W., Bellshaw, D., Zotev, N., Lane, T., Liang, M., Minitti, M., Boutet, S., Kirrander, A., Weber, P. AMER CHEMICAL SOC. 2018

  View details for Web of Science ID 000447609103463

• Determining Orientations of Optical Transition Dipole Moments using Ultrafast X-Ray Scattering. The journal of physical chemistry letters Yong, H. n., Zotev, N. n., Stankus, B. n., Ruddock, J. M., Bellshaw, D. n., Boutet, S. n., Lane, T. J., Liang, M. n., Carbajo, S. n., Robinson, J. S., Du, W. n., Goff, N. n., Chang, Y. n., Koglin, J. E., Waters, M. D., Sølling, T. I., Minitti, M. P., Kirrander, A. n., Weber, P. M. 2018

  Abstract

  The identification of the initially prepared, optically active state remains a challenging problem in many studies of ultrafast photoinduced processes. We show that the initially excited electronic state can be determined using the anisotropic component of ultrafast time-resolved X-ray scattering signals. The concept is demonstrated using the time-dependent X-ray scattering of N-methyl morpholine in the gas-phase upon excitation by a 200 nm linearly polarized optical pulse. Analysis of the angular dependence of the scattering signal near time zero renders the orientation of the transition dipole moment in the molecular frame and identifies the initially excited state as the 3pz Rydberg state, thus bypassing the need for further experimental studies to determine the starting point of the photoinduced dynamics and clarifying inconsistent computational results.

  View details for PubMedID 30380873

• L-edge spectroscopy of dilute, radiation-sensitive systems using a transition-edge-sensor array JOURNAL OF CHEMICAL PHYSICS Titus, C. J., Baker, M. L., Lee, S., Cho, H., Doriese, W. B., Fowler, J. W., Gaffney, K., Gard, J. D., Hilton, G. C., Kenney, C., Knight, J., Li, D., Marks, R., Minitti, M. P., Morgan, K. M., O'Neil, G. C., Reintsema, C. D., Schmidt, D. R., Sokaras, D., Swetz, D. S., Ullom, J. N., Weng, T., Williams, C., Young, B. A., Irwin, K. D., Solomon, E. I., Nordlund, D. 2017; 147 (21): 214201

  Abstract

  We present X-ray absorption spectroscopy and resonant inelastic X-ray scattering (RIXS) measurements on the iron L-edge of 0.5 mM aqueous ferricyanide. These measurements demonstrate the ability of high-throughput transition-edge-sensor (TES) spectrometers to access the rich soft X-ray (100-2000 eV) spectroscopy regime for dilute and radiation-sensitive samples. Our low-concentration data are in agreement with high-concentration measurements recorded by grating spectrometers. These results show that soft-X-ray RIXS spectroscopy acquired by high-throughput TES spectrometers can be used to study the local electronic structure of dilute metal-centered complexes relevant to biology, chemistry, and catalysis. In particular, TES spectrometers have a unique ability to characterize frozen solutions of radiation- and temperature-sensitive samples.

  View details for PubMedID 29221417

  View details for PubMedCentralID PMC5720893

• Nonlinear Ultrafast Spin Scattering in the Skyrmion Phase of Cu2OSeO3 PHYSICAL REVIEW LETTERS Langner, M. C., Roy, S., Huang, S. W., Koralek, J. D., Chuang, Y., Dakovski, G. L., Turner, J. J., Robinson, J. S., Coffee, R. N., Minitti, M. P., Seki, S., Tokura, Y., Schoenlein, R. W. 2017; 119 (10): 107204

  Abstract

  Ultrafast x-ray scattering studies of the topological Skyrmion phase in Cu_{2}OSeO_{3} show the dynamics to be strongly dependent on the excitation energy and fluence. At high photon energies, where the electron-spin scattering cross section is relatively high, the excitation of the topological Skyrmion phase shows a nonlinear dependence on the excitation fluence, in contrast to the excitation of the conical phase which is linearly dependent on the excitation fluence. The excitation of the Skyrmion order parameter is nonlinear in the magnetic excitation resulting from scattering during electron-hole recombination, indicating different dominant scattering processes in the conical and Skyrmion phases.

  View details for DOI 10.1103/PhysRevLett.119.107204

  View details for Web of Science ID 000409560100006

  View details for PubMedID 28949160

• Soft x-ray absorption spectroscopy of metalloproteins and high-valent metal-complexes at room temperature using free-electron lasers STRUCTURAL DYNAMICS Kubin, M., Kern, J., Gul, S., Kroll, T., Chatterjee, R., Loechel, H., Fuller, F. D., Sierra, R. G., Quevedo, W., Weniger, C., Rehanek, J., Firsov, A., Laksmono, H., Weninger, C., Alonso-Mori, R., Nordlund, D. L., Lassalle-Kaiser, B., Glownia, J. M., Krzywinski, J., Moeller, S., Turner, J. J., Minitti, M. P., Dakovski, G. L., Koroidov, S., Kawde, A., Kanady, J. S., Tsui, E. Y., Suseno, S., Han, Z., Hill, E., Taguchi, T., Borovik, A. S., Agapie, T., Messinger, J., Erko, A., Foehlisch, A., Bergmann, U., Mitzner, R., Yachandra, V. K., Yano, J., Wernet, P. 2017; 4 (5): 054307

  Abstract

  X-ray absorption spectroscopy at the L-edge of 3d transition metals provides unique information on the local metal charge and spin states by directly probing 3d-derived molecular orbitals through 2p-3d transitions. However, this soft x-ray technique has been rarely used at synchrotron facilities for mechanistic studies of metalloenzymes due to the difficulties of x-ray-induced sample damage and strong background signals from light elements that can dominate the low metal signal. Here, we combine femtosecond soft x-ray pulses from a free-electron laser with a novel x-ray fluorescence-yield spectrometer to overcome these difficulties. We present L-edge absorption spectra of inorganic high-valent Mn complexes (Mn ∼ 6-15 mmol/l) with no visible effects of radiation damage. We also present the first L-edge absorption spectra of the oxygen evolving complex (Mn4CaO5) in Photosystem II (Mn < 1 mmol/l) at room temperature, measured under similar conditions. Our approach opens new ways to study metalloenzymes under functional conditions.

  View details for PubMedID 28944255

• Measurements of the K-Shell Opacity of a Solid-Density Magnesium Plasma Heated by an X-Ray Free-Electron Laser PHYSICAL REVIEW LETTERS Preston, T. R., Vinko, S. M., Ciricosta, O., Hollebon, P., Chung, H., Dakovski, G. L., Krzywinski, J., Minitti, M., Burian, T., Chalupsky, J., Hajkova, V., Juha, L., Vozda, V., Zastrau, U., Lee, R. W., Wark, J. S. 2017; 119 (8): 085001

  Abstract

  We present measurements of the spectrally resolved x rays emitted from solid-density magnesium targets of varying sub-μm thicknesses isochorically heated by an x-ray laser. The data exhibit a largely thickness-independent source function, allowing the extraction of a measure of the opacity to K-shell x rays within well-defined regimes of electron density and temperature, extremely close to local thermodynamic equilibrium conditions. The deduced opacities at the peak of the Kα transitions of the ions are consistent with those predicted by detailed atomic-kinetics calculations.

  View details for DOI 10.1103/PhysRevLett.119.085001

  View details for Web of Science ID 000408354800009

  View details for PubMedID 28952743

• Real-Time Elucidation of Catalytic Pathways in CO Hydrogenation on Ru JOURNAL OF PHYSICAL CHEMISTRY LETTERS LaRue, J., Krejci, O., Yu, L., Beye, M., Ng, M. L., Oberg, H., Xin, H., Mercurio, G., Moeller, S., Turner, J. J., Nordlund, D., Coffee, R., Minitti, M. P., Wurth, W., Pettersson, L. M., Ostrom, H., Nilsson, A., Abild-Pedersen, F., Ogasawara, H. 2017; 8 (16): 3820–25

  Abstract

  The direct elucidation of the reaction pathways in heterogeneous catalysis has been challenging due to the short-lived nature of reaction intermediates. Here, we directly measured on ultrafast time scales the initial hydrogenation steps of adsorbed CO on a Ru catalyst surface, which is known as the bottleneck reaction in syngas and CO2 reforming processes. We initiated the hydrogenation of CO with an ultrafast laser temperature jump and probed transient changes in the electronic structure using real-time X-ray spectroscopy. In combination with theoretical simulations, we verified the formation of CHO during CO hydrogenation.

  View details for PubMedID 28759996

• The Linac Coherent Light Source: Recent Developments and Future Plans APPLIED SCIENCES-BASEL Schoenlein, R. W., Boutet, S., Minitti, M. P., Dunne, A. M. 2017; 7 (8)

  View details for DOI 10.3390/app7080850

  View details for Web of Science ID 000408905900100

• Ultrafast Independent N-H and N-C Bond Deformation Investigated with Resonant Inelastic X-Ray Scattering ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Eckert, S., Norell, J., Miedema, P. S., Beye, M., Fondell, M., Quevedo, W., Kennedy, B., Hantschmann, M., Pietzsch, A., Van Kuiken, B. E., Ross, M., Minitti, M. P., Moeller, S. P., Schlotter, W. F., Khalil, M., Odelius, M., Foehlisch, A. 2017; 56 (22): 6088–92

  Abstract

  The femtosecond excited-state dynamics following resonant photoexcitation enable the selective deformation of N-H and N-C chemical bonds in 2-thiopyridone in aqueous solution with optical or X-ray pulses. In combination with multiconfigurational quantum-chemical calculations, the orbital-specific electronic structure and its ultrafast dynamics accessed with resonant inelastic X-ray scattering at the N 1s level using synchrotron radiation and the soft X-ray free-electron laser LCLS provide direct evidence for this controlled photoinduced molecular deformation and its ultrashort timescale.

  View details for PubMedID 28374523

  View details for PubMedCentralID PMC5485001

• Determination of differential orbital covalency of heme active sites by L-edge spectroscopy Baker, M., Alpert, B., Cho, H., Denison, E., Doriese, W., Fowler, J., Gaffney, K., Gard, J., Gao, B., Hilton, G., Irwin, K., Joe, Y., Kenney, C., Knight, J., Kroll, T., Lee, S., Li, D., Marks, R., Minitti, M., Morgan, K., Mori, R., Ogasawara, H., O'Neil, G., Schmidt, D., Sokaras, D., Swetz, D., Song, Y., Titus, C., Ullom, J., Weng, T., Williams, C., Yan, J., Young, B., Nordlund, D., Solomon, E. AMER CHEMICAL SOC. 2017

  View details for Web of Science ID 000430569103813

• Ultrasensitive probing of the local electronic structure of nitrogen doped carbon and its applications to 2D electronics, catalysis and bio-physics Lee, S., Mori, R., Alpert, B., Baker, M., Berry, J., Cho, H., Denison, E., Doriese, W., Fowler, J., Gaffney, K., Gao, B., Gard, J., Hilton, G., Irwin, K., Joe, Y., Kaya, S., Kenney, C., Knight, J., Kroll, T., Li, D., Marks, R., Minitti, M., Morgan, K., Nordlund, D., O'Neil, G., Ogasawara, H., Pianetta, P., Reintsema, C., Schiros, T., Schmidt, D., Sokaras, D., Song, Y., Swetz, D., Titus, C., Ullom, J., Weng, T., Williams, C., Wolcott, A., Young, B. AMER CHEMICAL SOC. 2017

  View details for Web of Science ID 000430568506218

• Probing the local electronic structure of dilute bioinorganic active sites using ultra-sensitive soft X-ray detectors Titus, C., Alpert, B., Baker, M., Cho, H., Denison, E., Doriese, W., Fowler, J., Gaffney, K., Gao, B., Gard, J., Hilton, G., Irwin, K., Joe, Y., Kenney, C., Knight, J., Kroll, T., Lee, S., Li, D., Minitti, M., Morgan, K., Mori, R., Nordlund, D., O'Neil, G., Ogasawara, H., Reintsema, C., Schmidt, D., Sokaras, D., Song, Y., Swetz, D., Ullom, J., Weng, T., Williams, C., Young, B. AMER CHEMICAL SOC. 2017

  View details for Web of Science ID 000430568501597

• Ultra sensitive probing of the local electronic structure based on state-of-the-art Transition-Edge Sensor (TES) technology and soft x-ray spectroscopy Nordlund, D., Alpert, B., Baker, M., Cho, H., Denison, E., Doriese, W., Fowler, J., Gaffney, K., Gao, B., Gard, J., Hilton, G., Irwin, K., Joe, Y., Kenney, C., Knight, J., Kroll, T., Lee, S., Li, D., Marks, R., Minitti, M., Mori, R., Ogasawara, H., O'Neil, G., Schmidt, D., Sokaras, D., Swetz, D., Song, Y., Titus, C., Ullom, J., Weng, T., Williams, C., Young, B. AMER CHEMICAL SOC. 2017

  View details for Web of Science ID 000430568502277

• Nonequilibrium lattice-driven dynamics of stripes in nickelates using time-resolved x-ray scattering PHYSICAL REVIEW B Lee, W. S., Kung, Y. F., Moritz, B., Coslovich, G., Kaindl, R. A., Chuang, Y. D., Moore, R. G., Lu, D. H., Kirchmann, P. S., ROBINSON, J. S., Minitti, M. P., Dakovski, G., Schlotter, W. F., Turner, J. J., Gerber, S., Sasagawa, T., Hussain, Z., Shen, Z. X., Devereaux, T. P. 2017; 95 (12)

  View details for DOI 10.1103/PhysRevB.95.121105

  View details for Web of Science ID 000396014600002

• Femtosecond photodissociation dynamics of 1,4-diiodobenzene by gas-phase X-ray scattering and photoelectron spectroscopy. Faraday discussions Stankus, B., Budarz, J. M., Kirrander, A., Rogers, D., Robinson, J., Lane, T. J., Ratner, D., Hastings, J., Minitti, M. P., Weber, P. M. 2016: -?

  Abstract

  We present a multifaceted investigation into the initial photodissociation dynamics of 1,4-diiodobenzene (DIB) following absorption of 267 nm radiation. We combine ultrafast time-resolved photoelectron spectroscopy and X-ray scattering experiments performed at the Linac Coherent Light Source (LCLS) to study the initial electronic excitation and subsequent rotational alignment, and interpret the experiments in light of Complete Active Space Self-Consistent Field (CASSCF) calculations of the excited electronic landscape. The initially excited state is found to be a bound (1)B1 surface, which undergoes ultrafast population transfer to a nearby state in 35 ± 10 fs. The internal conversion most likely leads to one or more singlet repulsive surfaces that initiate the dissociation. This initial study is an essential and prerequisite component of a comprehensive study of the complete photodissociation pathway(s) of DIB at 267 nm. Assignment of the initially excited electronic state as a bound state identifies the mechanism as predissociative, and measurement of its lifetime establishes the time between excitation and initiation of dissociation, which is crucial for direct comparison of photoelectron and scattering experiments.

  View details for PubMedID 27711844

• Chemical Bond Activation Observed with an X-ray Laser JOURNAL OF PHYSICAL CHEMISTRY LETTERS Beye, M., Oberg, H., Xin, H., Dakovski, G. L., Dell'Angela, M., Foehlisch, A., Gladh, J., Hantschmann, M., Hieke, F., Kaya, S., Kuehn, D., LaRue, J., Mercurio, G., Minitti, M. P., Mitra, A., Moeller, S. P., Ng, M. L., Nilsson, A., Nordlund, D., Norskov, J., Ostrom, H., Ogasawara, H., Persson, M., Schlotter, W. F., Sellberg, J. A., Wolf, M., Abild-Pedersen, F., Pettersson, L. G., Wurth, W. 2016; 7 (18): 3647-3651

  Abstract

  The concept of bonding and antibonding orbitals is fundamental in chemistry. The population of those orbitals and the energetic difference between the two reflect the strength of the bonding interaction. Weakening the bond is expected to reduce this energetic splitting, but the transient character of bond-activation has so far prohibited direct experimental access. Here we apply time-resolved soft X-ray spectroscopy at a free-electron laser to directly observe the decreased bonding-antibonding splitting following bond-activation using an ultrashort optical laser pulse.

  View details for DOI 10.1021/acs.jpclett.6b01543

  View details for Web of Science ID 000383641800019

• Chemical Bond Activation Observed with an X-ray Laser. journal of physical chemistry letters Beye, M., Öberg, H., Xin, H., Dakovski, G. L., Dell'Angela, M., Föhlisch, A., Gladh, J., Hantschmann, M., Hieke, F., Kaya, S., Kühn, D., LaRue, J., Mercurio, G., Minitti, M. P., Mitra, A., Moeller, S. P., Ng, M. L., Nilsson, A., Nordlund, D., Nørskov, J., Öström, H., Ogasawara, H., Persson, M., Schlotter, W. F., Sellberg, J. A., Wolf, M., Abild-Pedersen, F., Pettersson, L. G., Wurth, W. 2016; 7 (18): 3647-3651

  Abstract

  The concept of bonding and antibonding orbitals is fundamental in chemistry. The population of those orbitals and the energetic difference between the two reflect the strength of the bonding interaction. Weakening the bond is expected to reduce this energetic splitting, but the transient character of bond-activation has so far prohibited direct experimental access. Here we apply time-resolved soft X-ray spectroscopy at a free-electron laser to directly observe the decreased bonding-antibonding splitting following bond-activation using an ultrashort optical laser pulse.

  View details for DOI 10.1021/acs.jpclett.6b01543

  View details for PubMedID 27584914

• Ultrafast dynamics of localized magnetic moments in the unconventional Mott insulator Sr2IrO4 JOURNAL OF PHYSICS-CONDENSED MATTER Krupin, O., Dakovski, G. L., Kim, B. J., Kim, J. W., Kim, J., Mishra, S., Chuang, Y., Serrao, C. R., Lee, W., Schlotter, W. F., Minitti, M. P., Zhu, D., Fritz, D., Chollet, M., Ramesh, R., Molodtsov, S. L., Turner, J. J. 2016; 28 (32)

  Abstract

  We report a time-resolved study of the ultrafast dynamics of the magnetic moments formed by the [Formula: see text] states in Sr2IrO4 by directly probing the localized iridium 5d magnetic state through resonant x-ray diffraction. Using optical pump-hard x-ray probe measurements, two relaxation time scales were determined: a fast fluence-independent relaxation is found to take place on a time scale of 1.5 ps, followed by a slower relaxation on a time scale of 500 ps-1.5 ns.

  View details for DOI 10.1088/0953-8984/28/32/32LT01

  View details for Web of Science ID 000378845900001

  View details for PubMedID 27310659

• Indirect excitation of ultrafast demagnetization. Scientific reports Vodungbo, B., Tudu, B., Perron, J., Delaunay, R., Müller, L., Berntsen, M. H., Grübel, G., Malinowski, G., Weier, C., Gautier, J., Lambert, G., Zeitoun, P., Gutt, C., Jal, E., Reid, A. H., Granitzka, P. W., Jaouen, N., Dakovski, G. L., Moeller, S., Minitti, M. P., Mitra, A., Carron, S., Pfau, B., von Korff Schmising, C., Schneider, M., Eisebitt, S., Lüning, J. 2016; 6: 18970-?

  Abstract

  Does the excitation of ultrafast magnetization require direct interaction between the photons of the optical pump pulse and the magnetic layer? Here, we demonstrate unambiguously that this is not the case. For this we have studied the magnetization dynamics of a ferromagnetic cobalt/palladium multilayer capped by an IR-opaque aluminum layer. Upon excitation with an intense femtosecond-short IR laser pulse, the film exhibits the classical ultrafast demagnetization phenomenon although only a negligible number of IR photons penetrate the aluminum layer. In comparison with an uncapped cobalt/palladium reference film, the initial demagnetization of the capped film occurs with a delayed onset and at a slower rate. Both observations are qualitatively in line with energy transport from the aluminum layer into the underlying magnetic film by the excited, hot electrons of the aluminum film. Our data thus confirm recent theoretical predictions.

  View details for DOI 10.1038/srep18970

  View details for PubMedID 26733106

  View details for PubMedCentralID PMC4702181

• Attosecond processes and X-ray spectroscopy: general discussion FARADAY DISCUSSIONS Milne, C. J., Weber, P. M., Kowalewski, M., Marangos, J. P., Johnson, A. S., Forbes, R., Worner, H., Rolles, D., Townsend, D., Schalk, O., Mai, S., Vacher, M., Miller, R., Centurion, M., Vibok, A., Domcke, W., Cireasa, R., Ueda, K., Bencivenga, F., Neumark, D. M., Stolow, A., Rudenko, A., Kirrander, A., Dowek, D., Martin, F., Ivanov, M., Dahlstrom, J., Dudovich, N., Mukamel, S., Sanchez-Gonzalez, A., Minitti, M. P., Austin, D. R., Kimberg, V., Masin, Z. 2016; 194: 427–62

  View details for DOI 10.1039/c6fd90071b

  View details for Web of Science ID 000392422200019

  View details for PubMedID 27901538

• Electronic and non-adiabatic dynamics: general discussion FARADAY DISCUSSIONS Orr-Ewing, A. J., Verlet, J. R., Penfold, T. J., Minns, R. S., Minitti, M. P., Solling, T. I., Schalk, O., Kowalewski, M., Marangos, J. P., Robb, M. A., Johnson, A. S., Worner, H., Shalashilin, D. V., Miller, R., Domcke, W., Ueda, K., Weber, P. M., Cireasa, R., Vacher, M., Roberts, G. M., Decleva, P., Bencivenga, F., Neumark, D. M., Gessner, O., Stolow, A., Mishra, P., Polyak, I., Baeck, K., Kirrander, A., Dowek, D., Jimenez-Galan, A., Martin, F., Mukamel, S., Sekikawa, T., Gelin, M. F., Townsend, D., Makhov, D. V., Neville, S. P. 2016; 194: 209–57

  View details for DOI 10.1039/c6fd90070d

  View details for Web of Science ID 000392422200011

  View details for PubMedID 27896343

• Structural dynamics: general discussion FARADAY DISCUSSIONS Decleva, P., Orr-Ewing, A. J., Kowalewski, M., Kornilov, O., Marangos, J. P., Worner, H., Johnson, A. S., Forbes, R., Rolles, D., Townsend, D., Schalk, O., Mai, S., Penfold, T. J., Miller, R., Centurion, M., Ueda, K., Domcke, W., Weber, P. M., Baeck, K., Travnikova, O., Liekhus-Schmaltz, C., Figueira, J., Neumark, N. M., Gessner, O., Stolow, A., Rudenko, A., Mishra, P., Kirrander, A., Dowek, D., Martin, F., Vibok, A., Minitti, M. P., Stankus, B., Burger, C. 2016; 194: 583–620

  View details for DOI 10.1039/c6fd90072k

  View details for Web of Science ID 000392422200027

  View details for PubMedID 27906385

• Vibrational and condensed phase dynamics: general discussion FARADAY DISCUSSIONS Orr-Ewing, A. J., Kornilov, O., Solling, T. I., Keane, T., Minitti, M. P., Worner, H., Schalk, O., Roberts, G. M., Minns, R. S., Milne, C. J., Miseikis, L., Penfold, T. J., Miller, R., Domcke, W., Centurion, M., Ueda, K., Weber, P. M., Gessner, O., Neumark, D. M., Stolow, A., Yano, J., Mukamel, S., Stavros, V. G. 2016; 194: 747–75

  View details for DOI 10.1039/c6fd90073a

  View details for Web of Science ID 000392422200034

  View details for PubMedID 27901160

• Magnetic order dynamics in optically excited multiferroic TbMnO3 PHYSICAL REVIEW B Johnson, J. A., Kubacka, T., Hoffmann, M. C., Vicario, C., de Jong, S., Beaud, P., Gruebel, S., Huang, S., Huber, L., Windsor, Y. W., Bothschafter, E. M., Rettig, L., Ramakrishnan, M., Alberca, A., Patthey, L., Chuang, Y., Turner, J. J., Dakovski, G. L., Lee, W., Minitti, M. P., Schlotter, W., Moore, R. G., Hauri, C. P., Koohpayeh, S. M., Scagnoli, V., Ingold, G., Johnson, S. L., Staub, U. 2015; 92 (18)

  View details for DOI 10.1103/PhysRevB.92.184429

  View details for Web of Science ID 000365773100008

• Imaging Molecular Motion: Femtosecond X-Ray Scattering of an Electrocyclic Chemical Reaction PHYSICAL REVIEW LETTERS Minitti, M. P., Budarz, J. M., Kirrander, A., ROBINSON, J. S., Ratner, D., Lane, T. J., Zhu, D., Glownia, J. M., Kozina, M., Lemke, H. T., Sikorski, M., Feng, Y., Nelson, S., Saita, K., Stankus, B., Northey, T., Hastings, J. B., Weber, P. M. 2015; 114 (25)

  Abstract

  Structural rearrangements within single molecules occur on ultrafast time scales. Many aspects of molecular dynamics, such as the energy flow through excited states, have been studied using spectroscopic techniques, yet the goal to watch molecules evolve their geometrical structure in real time remains challenging. By mapping nuclear motions using femtosecond x-ray pulses, we have created real-space representations of the evolving dynamics during a well-known chemical reaction and show a series of time-sorted structural snapshots produced by ultrafast time-resolved hard x-ray scattering. A computational analysis optimally matches the series of scattering patterns produced by the x rays to a multitude of potential reaction paths. In so doing, we have made a critical step toward the goal of viewing chemical reactions on femtosecond time scales, opening a new direction in studies of ultrafast chemical reactions in the gas phase.

  View details for DOI 10.1103/PhysRevLett.114.255501

  View details for Web of Science ID 000356586100002

  View details for PubMedID 26197134

• Combining THz laser excitation with resonant soft X-ray scattering at the Linac Coherent Light Source JOURNAL OF SYNCHROTRON RADIATION Turner, J. J., Dakovski, G. L., Hoffmann, M. C., Hwang, H. Y., Zarem, A., Schlotter, W. F., Moeller, S., Minitti, M. P., Staub, U., Johnson, S., Mitra, A., Swiggers, M., Noonan, P., Curiel, G. I., Holmes, M. 2015; 22: 621-625

  Abstract

  This paper describes the development of new instrumentation at the Linac Coherent Light Source for conducting THz excitation experiments in an ultra high vacuum environment probed by soft X-ray diffraction. This consists of a cantilevered, fully motorized mirror system which can provide 600 kV cm(-1) electric field strengths across the sample and an X-ray detector that can span the full Ewald sphere with in-vacuum motion. The scientific applications motivated by this development, the details of the instrument, and spectra demonstrating the field strengths achieved using this newly developed system are discussed.

  View details for DOI 10.1107/S1600577515005998

  View details for Web of Science ID 000353920300024

  View details for PubMedID 25931077

  View details for PubMedCentralID PMC4416678

• Optical laser systems at the Linac Coherent Light Source JOURNAL OF SYNCHROTRON RADIATION Minitti, M. P., Robinson, J. S., Coffee, R. N., Edstrom, S., Gilevich, S., Glownia, J. M., Granados, E., Hering, P., Hoffmann, M. C., Miahnahri, A., Milathianaki, D., Polzin, W., Ratner, D., Tavella, F., Vetter, S., Welch, M., White, W. E., Fry, A. R. 2015; 22: 526–31

  Abstract

  Ultrafast optical lasers play an essential role in exploiting the unique capabilities of recently commissioned X-ray free-electron laser facilities such as the Linac Coherent Light Source (LCLS). Pump-probe experimental techniques reveal ultrafast dynamics in atomic and molecular processes and reveal new insights in chemistry, biology, material science and high-energy-density physics. This manuscript describes the laser systems and experimental methods that enable cutting-edge optical laser/X-ray pump-probe experiments to be performed at LCLS.

  View details for PubMedID 25931064

  View details for PubMedCentralID PMC4416671

• The Soft X-ray Research instrument at the Linac Coherent Light Source JOURNAL OF SYNCHROTRON RADIATION Dakovski, G. L., Heimann, P., Holmes, M., Krupin, O., Minitti, M. P., Mitra, A., Moeller, S., Rowen, M., Schlotter, W. F., Turner, J. J. 2015; 22: 498–502

  Abstract

  The Soft X-ray Research instrument provides intense ultrashort X-ray pulses in the energy range 280-2000 eV. A diverse set of experimental stations may be installed to investigate a broad range of scientific topics such as ultrafast chemistry, highly correlated materials, magnetism, surface science, and matter under extreme conditions. A brief description of the main instrument components will be given, followed by some selected scientific highlights.

  View details for PubMedID 25931059

  View details for PubMedCentralID PMC4416666

• The Atomic, Molecular and Optical Science instrument at the Linac Coherent Light Source JOURNAL OF SYNCHROTRON RADIATION Ferguson, K. R., Bucher, M., Bozek, J. D., Carron, S., Castagna, J., Coffee, R., Curiel, G. I., Holmes, M., Krzywinski, J., Messerschmidt, M., Minitti, M., Mitra, A., Moeller, S., Noonan, P., Osipov, T., Schorb, S., Swiggers, M., Wallace, A., Yin, J., Bostedt, C. 2015; 22: 492-497

  Abstract

  The Atomic, Molecular and Optical Science (AMO) instrument at the Linac Coherent Light Source (LCLS) provides a tight soft X-ray focus into one of three experimental endstations. The flexible instrument design is optimized for studying a wide variety of phenomena requiring peak intensity. There is a suite of spectrometers and two photon area detectors available. An optional mirror-based split-and-delay unit can be used for X-ray pump-probe experiments. Recent scientific highlights illustrate the imaging, time-resolved spectroscopy and high-power density capabilities of the AMO instrument.

  View details for DOI 10.1107/S1600577515004646

  View details for Web of Science ID 000353920300005

  View details for PubMedID 25931058

  View details for PubMedCentralID PMC4416665

• Strong Influence of Coadsorbate Interaction on CO Desorption Dynamics on Ru(0001) Probed by Ultrafast X-Ray Spectroscopy and Ab Initio Simulations PHYSICAL REVIEW LETTERS Xin, H., LaRue, J., Oberg, H., Beye, M., Dell'Angela, M., Turner, J. J., Gladh, J., Ng, M. L., Sellberg, J. A., Kaya, S., Mercurio, G., HIEKE, F., Nordlund, D., Schlotter, W. F., Dakovski, G. L., Minitti, M. P., Foehlisch, A., Wolf, M., Wurth, W., Ogasawara, H., Norskov, J. K., Ostrom, H., Pettersson, L. G., Nilsson, A., Abild-Pedersen, E. 2015; 114 (15)

  Abstract

  We show that coadsorbed oxygen atoms have a dramatic influence on the CO desorption dynamics from Ru(0001). In contrast to the precursor-mediated desorption mechanism on Ru(0001), the presence of surface oxygen modifies the electronic structure of Ru atoms such that CO desorption occurs predominantly via the direct pathway. This phenomenon is directly observed in an ultrafast pump-probe experiment using a soft x-ray free-electron laser to monitor the dynamic evolution of the valence electronic structure of the surface species. This is supported with the potential of mean force along the CO desorption path obtained from density-functional theory calculations. Charge density distribution and frozen-orbital analysis suggest that the oxygen-induced reduction of the Pauli repulsion, and consequent increase of the dative interaction between the CO 5σ and the charged Ru atom, is the electronic origin of the distinct desorption dynamics. Ab initio molecular dynamics simulations of CO desorption from Ru(0001) and oxygen-coadsorbed Ru(0001) provide further insights into the surface bond-breaking process.

  View details for DOI 10.1103/PhysRevLett.114.156101

  View details for Web of Science ID 000352990700006

  View details for PubMedID 25933322

• Irreversible transformation of ferromagnetic ordered stripe domains in single-shot infrared-pump/resonant-x-ray-scattering-probe experiments PHYSICAL REVIEW B Bergeard, N., Schaffert, S., Lopez-Flores, V., Jaouen, N., Geilhufe, J., Guenther, C. M., Schneider, M., Graves, C., Wang, T., Wu, B., Scherz, A., Baumier, C., Delaunay, R., Fortuna, F., Tortarolo, M., Tudu, B., Krupin, O., Minitti, M. P., Robinson, J., Schlotter, W. F., Turner, J. J., Luening, J., Eisebitt, S., Boeglin, C. 2015; 91 (5)

  View details for DOI 10.1103/PhysRevB.91.054416

  View details for Web of Science ID 000351770800003

• Atomic-Scale Perspective of Ultrafast Charge Transfer at a Dye-Semiconductor Interface JOURNAL OF PHYSICAL CHEMISTRY LETTERS Siefermann, K. R., Pemmaraju, C. D., Neppl, S., Shavorskiy, A., Cordones, A. A., Vura-Weis, J., Slaughter, D. S., Sturm, F. P., Weise, F., Bluhm, H., Strader, M. L., Cho, H., Lin, M., Bacellar, C., Khurmi, C., Guo, J., Coslovich, G., Robinson, J. S., Kaindl, R. A., Schoenlein, R. W., Belkacem, A., Neumark, D. M., Leone, S. R., Nordlund, D., Ogasawara, H., Krupin, O., Turner, J. J., Schlotter, W. F., Holmes, M. R., Messerschmidt, M., Minitti, M. P., Gul, S., Zhang, J. Z., Huse, N., Prendergast, D., Gessner, O. 2014; 5 (15): 2753-2759

  Abstract

  Understanding interfacial charge-transfer processes on the atomic level is crucial to support the rational design of energy-challenge relevant systems such as solar cells, batteries, and photocatalysts. A femtosecond time-resolved core-level photoelectron spectroscopy study is performed that probes the electronic structure of the interface between ruthenium-based N3 dye molecules and ZnO nanocrystals within the first picosecond after photoexcitation and from the unique perspective of the Ru reporter atom at the center of the dye. A transient chemical shift of the Ru 3d inner-shell photolines by (2.3 ± 0.2) eV to higher binding energies is observed 500 fs after photoexcitation of the dye. The experimental results are interpreted with the aid of ab initio calculations using constrained density functional theory. Strong indications for the formation of an interfacial charge-transfer state are presented, providing direct insight into a transient electronic configuration that may limit the efficiency of photoinduced free charge-carrier generation.

  View details for DOI 10.1021/jz501264x

  View details for Web of Science ID 000340222200044

  View details for PubMedID 26277975

• Toward structural femtosecond chemical dynamics: imaging chemistry in space and time FARADAY DISCUSSIONS Minitti, M. P., Budarz, J. M., Kirrander, A., Robinson, J., Lane, T. J., Ratner, D., Saita, K., Northey, T., Stankus, B., Cofer-Shabica, V., Hastings, J., Weber, P. M. 2014; 171: 81-91

  Abstract

  We aim to observe a chemical reaction in real time using gas-phase X-ray diffraction. In our initial experiment at the Linac Coherent Light Source (LCLS), we investigated the model system 1,3-cyclohexadiene (CHD) at very low vapor pressures. This reaction serves as a benchmark for numerous transformations in organic synthesis and natural product biology. Excitation of CHD by an ultraviolet optical pulse initiates an electrocyclic reaction that transforms the closed ring system into the open-chain structure of 1,3,5-hexatriene. We describe technical points of the experimental method and present first results. We also outline an approach to analyze the data involving nonlinear least-square optimization routines that match the experimental observations with predicted diffraction patterns calculated from trajectories for nonadiabatic vibronic wave packets.

  View details for DOI 10.1039/c4fd00030g

  View details for Web of Science ID 000345529900004

  View details for PubMedID 25415842

• Ultrafast structural dynamics in Rydberg excited N,N,N ',N '-tetramethylethylenediamine: conformation dependent electron lone pair interaction and charge delocalization CHEMICAL SCIENCE Cheng, X., Zhang, Y., Deb, S., Minitti, M. P., Gao, Y., Jonsson, H., Weber, P. M. 2014; 5 (11): 4394–4403

  View details for DOI 10.1039/c4sc01646g

  View details for Web of Science ID 000343004300036

• L-Edge X-ray Absorption Spectroscopy of Dilute Systems Relevant to Metalloproteins Using an X-ray Free-Electron Laser JOURNAL OF PHYSICAL CHEMISTRY LETTERS Mitzner, R., Rehanek, J., Kern, J., Gul, S., Hattne, J., Taguchi, T., Alonso-Mori, R., Tran, R., Weniger, C., Schroeder, H., Quevedo, W., Laksmono, H., Sierra, R. G., Han, G., Lassalle-Kaiser, B., Koroidov, S., Kubicek, K., Schreck, S., Kunnus, K., Brzhezinskaya, M., Firsov, A., Minitti, M. P., Turner, J. J., Moeller, S., Sauter, N. K., Bogan, M. J., Nordlund, D., Schlotter, W. F., Messinger, J., Borovik, A., Techert, S., de Groot, F. M., Foehlisch, A., Erko, A., Bergmann, U., Yachandra, V. K., Wernet, P., Yano, J. 2013; 4 (21): 3641-3647

  Abstract

  L-edge spectroscopy of 3d transition metals provides important electronic structure information and has been used in many fields. However, the use of this method for studying dilute aqueous systems, such as metalloenzymes, has not been prevalent because of severe radiation damage and the lack of suitable detection systems. Here we present spectra from a dilute Mn aqueous solution using a high-transmission zone-plate spectrometer at the Linac Coherent Light Source (LCLS). The spectrometer has been optimized for discriminating the Mn L-edge signal from the overwhelming O K-edge background that arises from water and protein itself, and the ultrashort LCLS X-ray pulses can outrun X-ray induced damage. We show that the deviations of the partial-fluorescence yield-detected spectra from the true absorption can be well modeled using the state-dependence of the fluorescence yield, and discuss implications for the application of our concept to biological samples.

  View details for DOI 10.1021/jz401837f

  View details for Web of Science ID 000326845200010

  View details for PubMedCentralID PMC3901369

• L-Edge X-ray Absorption Spectroscopy of Dilute Systems Relevant to Metalloproteins Using an X-ray Free-Electron Laser. The journal of physical chemistry letters Mitzner, R., Rehanek, J., Kern, J., Gul, S., Hattne, J., Taguchi, T., Alonso-Mori, R., Tran, R., Weniger, C., Schröder, H., Quevedo, W., Laksmono, H., Sierra, R. G., Han, G., Lassalle-Kaiser, B., Koroidov, S., Kubicek, K., Schreck, S., Kunnus, K., Brzhezinskaya, M., Firsov, A., Minitti, M. P., Turner, J. J., Moeller, S., Sauter, N. K., Bogan, M. J., Nordlund, D., Schlotter, W. F., Messinger, J., Borovik, A., Techert, S., de Groot, F. M., Föhlisch, A., Erko, A., Bergmann, U., Yachandra, V. K., Wernet, P., Yano, J. 2013; 4 (21): 3641-3647

  Abstract

  L-edge spectroscopy of 3d transition metals provides important electronic structure information and has been used in many fields. However, the use of this method for studying dilute aqueous systems, such as metalloenzymes, has not been prevalent because of severe radiation damage and the lack of suitable detection systems. Here we present spectra from a dilute Mn aqueous solution using a high-transmission zone-plate spectrometer at the Linac Coherent Light Source (LCLS). The spectrometer has been optimized for discriminating the Mn L-edge signal from the overwhelming O K-edge background that arises from water and protein itself, and the ultrashort LCLS X-ray pulses can outrun X-ray induced damage. We show that the deviations of the partial-fluorescence yield-detected spectra from the true absorption can be well modeled using the state-dependence of the fluorescence yield, and discuss implications for the application of our concept to biological samples.

  View details for DOI 10.1021/jz401837f

  View details for PubMedID 24466387

  View details for PubMedCentralID PMC3901369

• Time-Resolved X-Ray Photoelectron Spectroscopy Techniques For Real-Time Studies Of Interfacial Charge Transfer Dynamics 22nd International Conference on the Application of Accelerators in Research and Industry (CAARI) Shavorskiy, A., Cordones, A., Vura-Weis, J., Siefermann, K., Slaughter, D., Sturm, F., Weise, F., Bluhm, H., Strader, M., Cho, H., Lin, M., Bacellar, C., Khurmi, C., Hertlein, M., Guo, J., Tyliszczak, T., Prendergast, D., Coslovich, G., Robinson, J., Kaindl, R. A., Schoenlein, R. W., Belkacem, A., Weber, T., Neumark, D. M., Leone, S. R., Nordlund, D., Ogasawara, H., Nilsson, A. R., Krupin, O., Turner, J. J., Schlotter, W. F., Holmes, M. R., Heimann, P. A., Messerschmidt, M., Minitti, M. P., Beye, M., Gul, S., Zhang, J. Z., Huse, N., Gessner, O. AMER INST PHYSICS. 2013: 475–479

  View details for DOI 10.1063/1.4802374

  View details for Web of Science ID 000319997900095

• Far-UV Photochemical Bond Cleavage of n-Amyl Nitrite: Bypassing a Repulsive Surface JOURNAL OF PHYSICAL CHEMISTRY A Minitti, M. P., Zhang, Y., Rosenberg, M., Brogaard, R. Y., Deb, S., Solling, T. I., Weber, P. M. 2012; 116 (2): 810–19

  Abstract

  We have investigated the deep-UV photoinduced, homolytic bond cleavage of amyl nitrite to form NO and pentoxy radicals. One-color multiphoton ionization with ultrashort laser pulses through the S(2) state resonance gives rise to photoelectron spectra that reflect ionization from the S(1) state. Time-resolved pump-probe photoionization measurements show that upon excitation at 207 nm, the generation of NO in the v = 2 state is delayed, with a rise time of 283 (16) fs. The time-resolved mass spectrum shows the NO to be expelled with a kinetic energy of 1.0 eV, which is consistent with dissociation on the S(1) state potential energy surface. Combined, these observations show that the first step of the dissociation reaction involves an internal conversion from the S(2) to the S(1) state, which is followed by the ejection of the NO radical on the predissociative S(1) state potential energy surface.

  View details for PubMedID 22175717

• Structural dynamics and energy flow in Rydberg-excited clusters of N,N-dimethylisopropylamine JOURNAL OF CHEMICAL PHYSICS Deb, S., Minitti, M. P., Weber, P. M. 2011; 135 (4): 044319

  Abstract

  In molecular beams, the tertiary amine N,N-dimethylisopropyl amine can form molecular clusters that are evident in photoelectron and mass spectra obtained upon resonant multiphoton ionization via the 3p and 3s Rydberg states. By delaying the ionization pulse from the excitation pulse we follow, in time, the ultrafast energy relaxation dynamics of the 3p to 3s internal conversion and the ensuing cluster evaporation, proton transfer, and structural dynamics. While evaporation of the cluster occurs in the 3s Rydberg state, proton transfer dominates on the ion surface. The mass-spectrum shows protonated species that arise from a proton transfer from the alpha-carbon of the neutral parent molecule to the N-atom of its ionized partner in the dimer. DFT calculations support the proton transfer mechanism between tightly bonded cluster components. The photoelectron spectrum shows broad peaks, ascribed to molecular clusters, which have an instantaneous shift of about 0.5 eV toward lower binding energies. That shift is attributed to the charge redistribution associated with the induced dipoles in surrounding cluster molecules. A time-dependent shift that decreases the Rydberg electron binding energy by a further 0.4 eV arises from the structural reorganization of the cluster solvent molecules as they react to the sudden creation of a charge.

  View details for PubMedID 21806131

• Structural Dynamics in Floppy Systems: Ultrafast Conformeric Motions in Rydberg-Excited Triethylamine JOURNAL OF PHYSICAL CHEMISTRY A Deb, S., Bayes, B. A., Minitti, M. P., Weber, P. M. 2011; 115 (10): 1804–9

  Abstract

  Rotations about its three carbon-nitrogen bonds give triethylamine a complex, 3-dimensional potential energy landscape of conformeric structures. Electronic excitation to Rydberg states prepares the molecule in a high-energy, nonequilibrium distribution of such conformers, initiating ultrafast transitions between them. Time-resolved Rydberg electron binding energy spectra, observed using photoionization-photoelectron spectroscopy with ultrashort laser pulses, reveal these time-evolving structures. The time-dependent structural fingerprint spectra are assigned with the aid of a computational analysis of the potential energy landscape. Upon 209 nm electronic excitation to the 3p Rydberg state, triethylamine decays to 3s with a 200 fs time constant. The initially prepared conformer reacts to a mixture of structures with a time constant of 232 fs and settles into a final geometry distribution on a further subpicosecond time scale. The binding energy of the Rydberg electron is found to be an important determinant of the conformeric energy landscape.

  View details for PubMedID 21338167

• Ring-Closing and Dehydrogenation Reactions of Highly Excited cis-Stilbene: Ultrafast Spectroscopy and Structural Dynamics JOURNAL OF PHYSICAL CHEMISTRY A Bao, J., Minitti, M. P., Weber, P. M. 2011; 115 (9): 1508–15

  Abstract

  The ultrafast dynamics of highly excited cis-stilbene (CS) in a molecular beam is explored using femtosecond time-resolved mass spectrometry and structure-sensitive photoelectron spectroscopy. cis-Stilbene is initially pumped by a 6 eV photon to the 7(1)B state and the reaction is followed by ionization with a time-delayed 3 eV probe pulse. Upon excitation, cis-stilbene rapidly decays to the 3(1)B state, where it undergoes a ring-closing reaction to form 4a,4b-dihydrophenanthrene (DHP). Whereas 14% of the ionized CS molecules dissociate one hydrogen atom to form hydrophenanthrene, the ionized DHP molecules completely dehydrogenate in the ion state to produce hydrophenanthrene and phenanthrene with a 1:1 ratio. We determined the lifetimes of the 7(1)B state and the 3(1)B state of CS to be 167 and 395 fs, respectively.

  View details for PubMedID 21309599

• Dissociative Energy Flow, Vibrational Energy Redistribution, and Conformeric Structural Dynamics in Bifunctional Amine Model Systems JOURNAL OF PHYSICAL CHEMISTRY A Bush, J. C., Minitti, M. P., Weber, P. M. 2010; 114 (42): 11078–84

  Abstract

  Time-resolved multiphoton ionization mass spectrometry coupled with Rydberg Fingerprint Spectroscopy (RFS) has been used to analyze the structural and electronic dynamics of N,N-dimethylphenethylamine (PENNA) and N,N-dimethylcyclohexethylamine (CENNA). In PENNA, the molecule converts from 3p to 3s on a time scale of 149 fs, a process that is reflected in the mass spectrum as the onset of fragmentation. Once in 3s, the overall signal intensity of the PENNA 3s signal shows biexponential decay kinetics, which is attributed to the electronic curve crossing from the Rydberg state to a dissociative antibonding orbital of the ethylenic bridge. This curve crossing exemplifies a possible fragmentation pathway observed in electron capture dissociation of proteins. The initially fast reaction (1.3 ps) is greatly slowed down as a result of an apparent relaxation process with a 5.6 ps time constant. The electron binding energy of the 3s Rydberg state of PENNA is observed to shift with a time constant of 4.8 ps, which is correlated to a cation-π interaction driven conformeric rearrangement.

  View details for PubMedID 20593860

• Structural dynamics of 1,3-Cyclohexadiene upon electrocyclic ring opening Buehler, C. C., Weber, P. M., Minitti, M. P., Deb, S., Bao, J. AMER CHEMICAL SOC. 2010

  View details for Web of Science ID 000208164706202

• Probing the Lifetimes of Internally Excited Amyl Nitrite Cations JOURNAL OF PHYSICAL CHEMISTRY A Rosenberg, M., Minitti, M. P., Rusteika, N., Bisgaard, C. Z., Deb, S., Weber, P. M., Solling, T. I. 2010; 114 (26): 7021–25

  Abstract

  The photoelectron spectrum shows that multiphoton ionization of amyl nitrite, C(5)H(11)ONO, using ultrafast laser pulses deposits up to 3.7 eV of energy into internal degrees of freedom. As a result, the molecules fragment to produce various daughter ions of masses 87, 71, 60, 57, 41, 30, 29, and 27. Absorption of an additional photon with 3 eV of energy by the ions yields transients with picosecond decay times, revealing the time scale of the decomposition dynamics of the initially prepared parent ion. Each mass peak has a distinct time constant, in the range of 1.2 to 7.9 ps, emphasizing the dependence of the fragmentation mechanism on the ion internal energy.

  View details for DOI 10.1021/jp102393g

  View details for Web of Science ID 000279282500013

  View details for PubMedID 20540545

• Ultrafast formation of an intramolecular cation-pi bond JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY Bush, J. C., Minitti, M. P., Weber, P. M. 2010; 213 (1): 70–72

  View details for DOI 10.1016/j.jphotochem.2010.05.001

  View details for Web of Science ID 000279969400010

• Ultrafast conformational dynamics of hot, Rydberg-excited triethylamine: Determined by the Rydberg electron Deb, S., Bayes, B. A., Minitti, M. P., Weber, P. M. AMER CHEMICAL SOC. 2010

  View details for Web of Science ID 000208189304314

• Ultrafast conformeric transformations of floppy molecules and reorganization of molecular clusters probed with Rydberg electrons Weber, P. M., Minitti, M. P. AMER CHEMICAL SOC. 2010

  View details for Web of Science ID 000208189304256

• N,N-Dimethylisopropyl amine clusters and ultrafast proton transfer dynamics Deb, S., Minitti, M. P., Weber, P. M. AMER CHEMICAL SOC. 2009

  View details for Web of Science ID 000207861909433

• Conformer dynamics in vibrationally hot tertiary amines probed with ultrafast Rydberg fingerprint spectroscopy Minitti, M. P., Deb, S., Bao, J., Weber, P. M. AMER CHEMICAL SOC. 2009

  View details for Web of Science ID 000207861909080

• Time-resolved conformational dynamics in hydrocarbon chains PHYSICAL REVIEW LETTERS Minitti, M. P., Weber, P. M. 2007; 98 (25): 253004

  Abstract

  Internal rotation about carbon-carbon bonds allows N,N-dimethyl-2-butanamine (DM2BA) and N,N-dimethyl-3-hexanamine (DM3HA) to assume multiple conformeric structures. We explore the equilibrium composition and dynamics between such conformeric structures using Rydberg fingerprint spectroscopy. Time constants for conformeric interconversion of DM2BA (at 1.79 eV of internal energy) are 19 and 66 ps, and for DM3HA (1.78 eV) 23 and 41 ps. For the first time, a time-resolved and quantitative view of conformational dynamics of flexible hydrocarbon molecules at high temperatures is revealed.

  View details for PubMedID 17678022

• Correlated product distributions from ketene dissociation measured by dc sliced ion imaging JOURNAL OF CHEMICAL PHYSICS Komissarov, A. V., Minitti, M. P., Suits, A. G., Hall, G. E. 2006; 124 (1): 14303

  Abstract

  Speed distributions of spectroscopically selected CO photoproducts of 308 nm ketene photodissociation have been measured by dc sliced ion imaging. Structured speed distributions are observed that match the clumps and gaps in the singlet CH2 rotational density of states. The effects of finite time gates in sliced ion imaging are important for the accurate treatment of quasicontinuous velocity distributions extending into the thickly sliced and fully projected regime, and an inversion algorithm has been implemented for the special case of isotropic fragmentation. With accurate velocity calibration and careful treatment of the velocity resolution, the new method allows us to characterize the coincident rotational state distribution of CH2 states as a smoothly varying deviation from an unbiased phase space theory (PST) limit, similar to a linear-surprisal analysis. High-energy rotational states of CH2 are underrepresented compared to PST in coincidence with all detected CO rotational states. There is no evidence for suppression of the fastest channels, as had been reported in two previous studies of this system by other techniques. The relative contributions of ground and first vibrationally excited singlet CH2 states in coincidence with selected rotational states of CO (upsilon=0) are well resolved and in remarkably good agreement with PST, despite large deviations from the PST rotational distributions in the CH2 fragments. At 308 nm, the singlet CH2 (upsilon2=0) and (upsilon2=1) channels are 2350 and 1000 cm(-1) above their respective thresholds. The observed vibrational branching is consistent with saturation at increasing energies of the energy-dependent suppression of rates with respect to the PST limit, attributed to a tightening variational transition state.

  View details for DOI 10.1063/1.2137312

  View details for Web of Science ID 000234428900017

  View details for PubMedID 16409032

• Rydberg fingerprint spectroscopy of hot molecules: structural dispersion in flexible hydrocarbons. The journal of physical chemistry. A Minitti, M. P., Cardoza, J. D., Weber, P. M. 2006; 110 (34): 10212–18

  Abstract

  We explore how structural dispersion in flexible hydrocarbon chain molecules at very high temperatures is reflected in the photoionization spectra of Rydberg levels. The spectra of N,N-dimethylisopropanamine, N,N-dimethyl-1-butanamine, N,N-dimethyl-2-butanamine, N,N-dimethyl-3-hexanamine, and 1,4-dimethylpiperazine, taken at effective vibrational temperatures of 700-1000 K, show well-resolved features stemming from the 3p and 3s Rydberg states. The line shapes observed in molecules with internal rotation degrees of freedom show that multiple structures are populated. Following up on the discovery that low-lying Rydberg states provide sensitive fingerprints of molecular structures, this work supports Rydberg fingerprint spectroscopy as a tool to probe structural details of molecules in the presence of complex energy landscapes and at high vibrational temperatures. A simple model accounts for the sensitivity of Rydberg fingerprint spectroscopy to the molecular shape, as well as the relative insensitivity of the spectra toward vibrational excitation.

  View details for PubMedID 16928110

• Energy flow and fragmentation dynamics of n,n-dimethylisopropylamine. The journal of physical chemistry. A Gosselin, J. L., Minitti, M. P., Rudakov, F. M., Sølling, T. I., Weber, P. M. 2006; 110 (12): 4251–55

  Abstract

  The energy flow and fragmentation dynamics of N,N-dimethylisopropylamine (DMIPA) upon excitation to the 3p Rydberg states has been investigated with use of time-resolved photoelectron and mass spectrometry. The 3p states are short-lived, with a lifetime of 701 +/- 45 fs. From the time dependence of the photoelectron spectra, we infer that the primary reaction channel leads to the 3s level, which itself decays to the ground state with a decay time of 87.9 +/- 10.2 ps. The mass spectrum reveals fragmentation with cleavage at the alpha C-C bond, indicating that the energy deposited in vibrations during the internal conversion from 3p to 3s exceeds the bond energy. A thorough examination of the binding energies and temporal dynamics of the Rydberg states, as well as a comparison to the related fragmentation of N,N-dimethyl-2-butanamine (DM2BA), suggests that the fragments are formed on the ion surfaces, i.e., after ionization and on a time scale much slower than the fluorescence decay from 3s to the ground state.

  View details for PubMedID 16553377

• Direct current slice imaging REVIEW OF SCIENTIFIC INSTRUMENTS Townsend, D., Minitti, M. P., Suits, A. G. 2003; 74 (4): 2530–39

  View details for DOI 10.1063/1.1544053

  View details for Web of Science ID 000181829000041