Bio


I am interested in photo-induced dynamics of atoms and molecules. I am particularly interested in the dynamics of excited states in these systems, and how energy transfer takes place inside a molecule. The relevant timescales for these interactions is typically in the range of attoseconds to picoseconds. These dynamics include photo-triggered chemistry such as non Born-Oppenheimer molecular dynamics and quantum phenomena in strong-field driven systems. I also develop tools for studying these dynamics in the time domain.

My research builds on my extensive experience with ultrafast optical laser science and technology. As a graduate student at Stanford University I participated in the first experiments at the Linac Coherent Light Source, where we studied a new regime of X-ray-matter interactions. I was a postdoctoral scholar at Lawerence Berkeley National Laboratory before returning to SLAC to lead the attosecond science group.

Education & Certifications


  • B.S., The Ohio State University, Engineering Physics (2007)
  • Ph.D., Stanford University, Physics (2012)

Professional Interests


I am interested in photo-induced dynamics of atoms and molecules. I am particularly interested in the dynamics of excited states in these systems, and how energy transfer takes place inside a molecule. The relevant timescales for these interactions is typically in the range of attoseconds to picoseconds. These dynamics include photo-triggered chemistry such as non Born-Oppenheimer molecular dynamics and quantum phenomena in strong-field driven systems. I also develop tools for studying these dynamics in the time domain.

Professional Affiliations and Activities


  • Principle Investigator, Stanford PULSE Institute (2014 - Present)
  • Soft X-ray Department Member, Linac Coherent Light Source, SLAC National Accelerator Laboratory (2017 - Present)

All Publications


  • Characterizing Multiphoton Excitation Using Time-Resolved X-ray Scattering PHYSICAL REVIEW X Bucksbaum, P. H., Ware, M. R., Natan, A., Cryan, J. P., Glownia, J. M. 2020; 10 (1)
  • Tunable isolated attosecond X-ray pulses with gigawatt peak power from a free-electron laser NATURE PHOTONICS Duris, J., Li, S., Driver, T., Champenois, E. G., MacArthur, J. P., Lutman, A. A., Zhang, Z., Rosenberger, P., Aldrich, J. W., Coffee, R., Coslovich, G., Decker, F., Glownia, J. M., Hartmann, G., Helml, W., Kamalov, A., Knurr, J., Krzywinski, J., Lin, M., Nantel, M., Natan, A., O'Neal, J., Shivaram, N., Walter, P., Wang, A., Welch, J. J., Wolf, T. A., Xu, J. Z., Kling, M. F., Bucksbaum, P. H., Zholents, A., Huang, Z., Cryan, J. P., Marinelli, A., Marangos, J. P. 2020; 14 (1): 30-+
  • Two-Photon Antenna Sensitization of Curium: Evidencing Metal-Driven Effects on Absorption Cross Section in f-Element Complexes. The journal of physical chemistry letters Pallares, R. M., Sturzbecher-Hoehne, M. n., Shivaram, N. H., Cryan, J. P., D'Aléo, A. n., Abergel, R. J. 2020: 6063–67

    Abstract

    Two-photon-excited fluorescence spectroscopy is a powerful tool to study the structural and electronic properties of optically active complexes and molecules. Although numerous lanthanide complexes have been characterized by two-photon-excited fluorescence in solution, this report is the first to apply such a technique to actinide compounds. Contrasting with previous observations in lanthanides, we demonstrate that the two-photon absorption properties of the complexes significantly depend on the metal (4f vs 5f), with Cm(III) complexes showing significantly higher two-photon absorption cross sections than lanthanide analogues and up to 200-fold stronger emission intensities. These results are consistent with electronic and structural differences between the lanthanide and actinide systems studied. Hence, the described methodology can provide valuable insights into the interactions between f-elements and ligands, along with promising prospects on the characterization of scarce compounds.

    View details for DOI 10.1021/acs.jpclett.0c01888

    View details for PubMedID 32635727

  • Electronic Population Transfer via Impulsive Stimulated X-Ray Raman Scattering with Attosecond Soft-X-Ray Pulses. Physical review letters O'Neal, J. T., Champenois, E. G., Oberli, S. n., Obaid, R. n., Al-Haddad, A. n., Barnard, J. n., Berrah, N. n., Coffee, R. n., Duris, J. n., Galinis, G. n., Garratt, D. n., Glownia, J. M., Haxton, D. n., Ho, P. n., Li, S. n., Li, X. n., MacArthur, J. n., Marangos, J. P., Natan, A. n., Shivaram, N. n., Slaughter, D. S., Walter, P. n., Wandel, S. n., Young, L. n., Bostedt, C. n., Bucksbaum, P. H., Picón, A. n., Marinelli, A. n., Cryan, J. P. 2020; 125 (7): 073203

    Abstract

    Free-electron lasers provide a source of x-ray pulses short enough and intense enough to drive nonlinearities in molecular systems. Impulsive interactions driven by these x-ray pulses provide a way to create and probe valence electron motions with high temporal and spatial resolution. Observing these electronic motions is crucial to understand the role of electronic coherence in chemical processes. A simple nonlinear technique for probing electronic motion, impulsive stimulated x-ray Raman scattering (ISXRS), involves a single impulsive interaction to produce a coherent superposition of electronic states. We demonstrate electronic population transfer via ISXRS using broad bandwidth (5.5 eV full width at half maximum) attosecond x-ray pulses produced by the Linac Coherent Light Source. The impulsive excitation is resonantly enhanced by the oxygen 1s→2π^{*} resonance of nitric oxide (NO), and excited state neutral molecules are probed with a time-delayed UV laser pulse.

    View details for DOI 10.1103/PhysRevLett.125.073203

    View details for PubMedID 32857563

  • Strictly non-adiabatic quantum control of the acetylene dication using an infrared field. The Journal of chemical physics Liekhus-Schmaltz, C. n., Zhu, X. n., McCracken, G. A., Cryan, J. P., Martinez, T. J., Bucksbaum, P. H. 2020; 152 (18): 184302

    Abstract

    We demonstrate the existence of a strictly non-adiabatic control pathway in deprotonation of the acetylene dication. This pathway is identified experimentally by measuring a kinetic energy shift in an ion coincidence experiment. We use a time dependent Schrödinger equation simulation to identify which properties most strongly affect our control. We find that resonant control around conical intersections is limited by the speed of non-adiabatic dynamics.

    View details for DOI 10.1063/5.0007058

    View details for PubMedID 32414271

  • Attosecond transient absorption spooktroscopy: a ghost imaging approach to ultrafast absorption spectroscopy. Physical chemistry chemical physics : PCCP Driver, T., Li, S., Champenois, E. G., Duris, J., Ratner, D., Lane, T. J., Rosenberger, P., Al-Haddad, A., Averbukh, V., Barnard, T., Berrah, N., Bostedt, C., Bucksbaum, P. H., Coffee, R., DiMauro, L. F., Fang, L., Garratt, D., Gatton, A., Guo, Z., Hartmann, G., Haxton, D., Helml, W., Huang, Z., LaForge, A., Kamalov, A., Kling, M. F., Knurr, J., Lin, M., Lutman, A. A., MacArthur, J. P., Marangos, J. P., Nantel, M., Natan, A., Obaid, R., O'Neal, J. T., Shivaram, N. H., Schori, A., Walter, P., Li Wang, A., Wolf, T. J., Marinelli, A., Cryan, J. P. 2019

    Abstract

    The recent demonstration of isolated attosecond pulses from an X-ray free-electron laser (XFEL) opens the possibility for probing ultrafast electron dynamics at X-ray wavelengths. An established experimental method for probing ultrafast dynamics is X-ray transient absorption spectroscopy, where the X-ray absorption spectrum is measured by scanning the central photon energy and recording the resultant photoproducts. The spectral bandwidth inherent to attosecond pulses is wide compared to the resonant features typically probed, which generally precludes the application of this technique in the attosecond regime. In this paper we propose and demonstrate a new technique to conduct transient absorption spectroscopy with broad bandwidth attosecond pulses with the aid of ghost imaging, recovering sub-bandwidth resolution in photoproduct-based absorption measurements.

    View details for DOI 10.1039/c9cp03951a

    View details for PubMedID 31793561

  • Development of ultrafast capabilities for X-ray free-electron lasers at the linac coherent light source PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES Coffee, R. N., Cryan, J. P., Duris, J., Helml, W., Li, S., Marinelli, A. 2019; 377 (2145)
  • Development of ultrafast capabilities for X-ray free-electron lasers at the linac coherent light source. Philosophical transactions. Series A, Mathematical, physical, and engineering sciences Coffee, R. N., Cryan, J. P., Duris, J., Helml, W., Li, S., Marinelli, A. 2019; 377 (2145): 20180386

    Abstract

    The ability to produce ultrashort, high-brightness X-ray pulses is revolutionizing the field of ultrafast X-ray spectroscopy. Free-electron laser (FEL) facilities are driving this revolution, but unique aspects of the FEL process make the required characterization and use of the pulses challenging. In this paper, we describe a number of developments in the generation of ultrashort X-ray FEL pulses, and the concomitant progress in the experimental capabilities necessary for their characterization and use at the Linac Coherent Light Source. This includes the development of sub-femtosecond hard and soft X-ray pulses, along with ultrafast characterization techniques for these pulses. We also describe improved techniques for optical cross-correlation as needed to address the persistent challenge of external optical laser synchronization with these ultrashort X-ray pulses. This article is part of the theme issue 'Measurement of ultrafast electronic and structural dynamics with X-rays'.

    View details for PubMedID 30929632

  • On the limits of observing motion in time-resolved X-ray scattering. Philosophical transactions. Series A, Mathematical, physical, and engineering sciences Ware, M. R., Glownia, J. M., Natan, A., Cryan, J. P., Bucksbaum, P. H. 2019; 377 (2145): 20170477

    Abstract

    Limits on the ability of time-resolved X-ray scattering (TRXS) to observe harmonic motion of amplitude, A and frequency, omega0, about an equilibrium position, R0, are considered. Experimental results from a TRXS experiment at the LINAC Coherent Light Source are compared to classical and quantum theories that demonstrate a fundamental limitation on the ability to observe the amplitude of motion. These comparisons demonstrate dual limits on the spatial resolution through Qmax and the temporal resolution through omegamax for observing the amplitude of motion. In the limit where omegamax omega0, the smallest observable amplitude of motion is A=2 pi/ Qmax. In the limit where omegamax≥2 omega0, A≤2 pi/ Qmax is observable provided there are sufficient statistics. This article is part of the theme issue 'Measurement of ultrafast electronic and structural dynamics with X-rays'.

    View details for PubMedID 30929636

  • On the limits of observing motion in time-resolved X-ray scattering PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES Ware, M. R., Glownia, J. M., Natan, A., Cryan, J. P., Bucksbaum, P. H. 2019; 377 (2145)
  • Ultrafast photodissociation dynamics and nonadiabatic coupling between excited electronic states of methanol probed by time-resolved photoelectron spectroscopy. The Journal of chemical physics Champenois, E. G., Greenman, L., Shivaram, N., Cryan, J. P., Larsen, K. A., Rescigno, T. N., McCurdy, C. W., Belkacem, A., Slaughter, D. S. 2019; 150 (11): 114301

    Abstract

    The electronic and nuclear dynamics in methanol, following 156 nm photoexcitation, are investigated by combining a detailed analysis of time-resolved photoelectron spectroscopy experiments with electronic structure calculations. The photoexcitation pump pulse is followed by a delayed 260 nm photoionization probe pulse to produce photoelectrons that are analyzed by velocity map imaging. The yields of mass-resolved ions, measured with similar experimental conditions, are found to exhibit the same time-dependence as specific photoelectron spectral features. Energy-resolved signal onset and decay times are extracted from the measured photoelectron spectra to achieve high temporal resolution, beyond the 20 fs pump and probe pulse durations. When combined with ab initio calculations of selected cuts through the excited state potential energy surfaces, this information allows the dynamics of the transient excited molecule, which exhibits multiple nuclear and electronic degrees of freedom, to be tracked on its intrinsic few-femtosecond time scale. Within 15 fs of photoexcitation, we observe nuclear motion on the initially bound photoexcited 21A (S2) electronic state, through a conical intersection with the 11A' (S3) state, which reveals paths to photodissociation following C-O stretch and C-O-H angle opening.

    View details for PubMedID 30902015

  • Generation and Characterization of Attosecond Pulses from an X-ray Free-electron Laser Li, S., Rosenberger, P., Champenois, E. G., Driver, T., Bucksbaum, P. H., Coffee, R., Gatton, A., Hartmann, G., Helml, W., Huang, Z., Knurr, J., Kling, M. F., Lin, M., MacArthur, J. P., Maxwell, T. J., Nantel, M., Natan, A., Oneal, J. T., Shivaram, N. H., Walter, P., Wolf, T. A., Cryan, J. P., Marinelli, A., IEEE IEEE. 2019
  • Characterizing isolated attosecond pulses with angular streaking OPTICS EXPRESS Li, S., Guo, Z., Coffee, R. N., Hegazy, K., Huang, Z., Natan, A., Osipov, T., Ray, D., Marinelli, A., Cryan, J. P. 2018; 26 (4): 4531–47

    Abstract

    We present a reconstruction algorithm for isolated attosecond pulses, which exploits the phase dependent energy modulation of a photoelectron ionized in the presence of a strong laser field. The energy modulation due to a circularly polarized laser field is manifest strongly in the angle-resolved photoelectron momentum distribution, allowing for complete reconstruction of the temporal and spectral profile of an attosecond burst. We show that this type of reconstruction algorithm is robust against counting noise and suitable for single-shot experiments. This algorithm holds potential for a variety of applications for attosecond pulse sources.

    View details for DOI 10.1364/OE.26.004531

    View details for Web of Science ID 000426268500073

    View details for PubMedID 29475303

  • Imaging CF3I conical intersection and photodissociation dynamics with ultrafast electron diffraction Science Yang, J., Zhu, X., Wolf, T. J., Li, Z., Nunes, J. F., Coffee, R., Cryan, J. P., Gühr, M., Hegazy, K., Heinz, T. F., Jobe, K., Li, R., Shen, X., Veccione, T., Weathersby, S., Wilkin, K. J., Yoneda, C., Zheng, Q., Martinez, T. J., Centurion, M., Wang, X. 2018; 361 (6397): 64-67

    View details for DOI 10.1126/science.aat0049

  • Imaging CF3I conical intersection and photodissociation dynamics with ultrafast electron diffraction. Science (New York, N.Y.) Yang, J. n., Zhu, X. n., Wolf, T. J., Li, Z. n., Nunes, J. P., Coffee, R. n., Cryan, J. P., Gühr, M. n., Hegazy, K. n., Heinz, T. F., Jobe, K. n., Li, R. n., Shen, X. n., Veccione, T. n., Weathersby, S. n., Wilkin, K. J., Yoneda, C. n., Zheng, Q. n., Martinez, T. J., Centurion, M. n., Wang, X. n. 2018; 361 (6397): 64–67

    Abstract

    Conical intersections play a critical role in excited-state dynamics of polyatomic molecules because they govern the reaction pathways of many nonadiabatic processes. However, ultrafast probes have lacked sufficient spatial resolution to image wave-packet trajectories through these intersections directly. Here, we present the simultaneous experimental characterization of one-photon and two-photon excitation channels in isolated CF3I molecules using ultrafast gas-phase electron diffraction. In the two-photon channel, we have mapped out the real-space trajectories of a coherent nuclear wave packet, which bifurcates onto two potential energy surfaces when passing through a conical intersection. In the one-photon channel, we have resolved excitation of both the umbrella and the breathing vibrational modes in the CF3 fragment in multiple nuclear dimensions. These findings benchmark and validate ab initio nonadiabatic dynamics calculations.

    View details for PubMedID 29976821

  • Ultrafast isomerization in acetylene dication after carbon K-shell ionization NATURE COMMUNICATIONS Li, Z., Inhester, L., Liekhus-Schmaltz, C., Curchod, B. E., Snyder, J. W., Medvedev, N., Cryan, J., Osipov, T., Pabst, S., Vendrell, O., Bucksbaum, P., Martinez, T. J. 2017; 8: 453

    Abstract

    Ultrafast proton migration and isomerization are key processes for acetylene and its ions. However, the mechanism for ultrafast isomerization of acetylene [HCCH]2+ to vinylidene [H2CC]2+ dication remains nebulous. Theoretical studies show a large potential barrier ( > 2 eV) for isomerization on low-lying dicationic states, implying picosecond or longer isomerization timescales. However, a recent experiment at a femtosecond X-ray free-electron laser suggests sub-100 fs isomerization. Here we address this contradiction with a complete theoretical study of the dynamics of acetylene dication produced by Auger decay after X-ray photoionization of the carbon atom K shell. We find no sub-100 fs isomerization, while reproducing the salient features of the time-resolved Coulomb imaging experiment. This work resolves the seeming contradiction between experiment and theory and also calls for careful interpretation of structural information from the widely applied Coulomb momentum imaging method.The timescale of isomerization in molecules involving ultrafast migration of constituent atoms is difficult to measure. Here the authors report that sub-100 fs isomerization time on acetylene dication in lower electronic states is not possible and point to misinterpretation of recent experimental results.

    View details for PubMedID 28878226

  • Observing Femtosecond Fragmentation Using Ultrafast X-ray-Induced Auger Spectra APPLIED SCIENCES-BASEL Wolf, T. A., Holzmeier, F., Wagner, I., Berrah, N., Bostedt, C., Bozek, J., Bucksbaum, P., Coffee, R., Cryan, J., Farrell, J., Feifel, R., Martinez, T. J., McFarland, B., Mucke, M., Nandi, S., Tarantelli, F., Fischer, I., Guhr, M. 2017; 7 (7)

    View details for DOI 10.3390/app7070681

    View details for Web of Science ID 000407700400038

  • Ultrafast dynamics of the lowest-lying neutral states in carbon dioxide PHYSICAL REVIEW A Wright, T. W., Champenois, E. G., Cryan, J. P., Shivaram, N., Yang, C., Belkacem, A. 2017; 95 (2)
  • Coherent control using kinetic energy and the geometric phase of a conical intersection. journal of chemical physics Liekhus-Schmaltz, C., McCracken, G. A., Kaldun, A., Cryan, J. P., Bucksbaum, P. H. 2016; 145 (14): 144304-?

    Abstract

    Conical intersections (CIs) between molecular potential energy surfaces with non-vanishing non-adiabatic couplings generally occur in any molecule consisting of at least three atoms. They play a fundamental role in describing the molecular dynamics beyond the Born-Oppenheimer approximation and have been used to understand a large variety of effects, from photofragmentation and isomerization to more exotic applications such as exciton fission in semiconductors. However, few studies have used the features of a CI as a tool for coherent control. Here we demonstrate two modes of control around a conical intersection. The first uses a continuous light field to control the population on the two intersecting electronic states in the vicinity of a CI. The second uses a pulsed light field to control wavepackets that are subjected to the geometric phase shift in transit around a CI. This second technique is likely to be useful for studying the role of nuclear dynamics in electronic coherence phenomena.

    View details for PubMedID 27782506

  • Coherent control using kinetic energy and the geometric phase of a conical intersection The Journal of Chemical Physics Liekhus-Schmaltz, C. E., McCracken, G. A., Kaldun, A., Cryan, J. P., Bucksbaum, P. H. 2016; 145: 144304

    Abstract

    Conical intersections (CIs) between molecular potential energy surfaces with non-vanishing non-adiabatic couplings generally occur in any molecule consisting of at least three atoms. They play a fundamental role in describing the molecular dynamics beyond the Born-Oppenheimer approximation and have been used to understand a large variety of effects, from photofragmentation and isomerization to more exotic applications such as exciton fission in semiconductors. However, few studies have used the features of a CI as a tool for coherent control. Here we demonstrate two modes of control around a conical intersection. The first uses a continuous light field to control the population on the two intersecting electronic states in the vicinity of a CI. The second uses a pulsed light field to control wavepackets that are subjected to the geometric phase shift in transit around a CI. This second technique is likely to be useful for studying the role of nuclear dynamics in electronic coherence phenomena.

    View details for DOI 10.1063/1.4964392

  • Involvement of a low-lying Rydberg state in the ultrafast relaxation dynamics of ethylene. The Journal of chemical physics Champenois, E. G., Shivaram, N. H., Wright, T. W., Yang, C. S., Belkacem, A. n., Cryan, J. P. 2016; 144 (1): 014303

    Abstract

    We present a measurement of the time-resolved photoelectron kinetic energy spectrum of ethylene using 156 nm and 260 nm laser pulses. The 156 nm pulse first excites ethylene to the (1)B1u (ππ(∗)) electronic state where 260 nm light photoionizes the system to probe the relaxation dynamics with sub-30 fs resolution. Recent ab initio calculations by Mori et al. [J. Phys. Chem. A 116, 2808-2818 (2012)] have predicted an ultrafast population transfer from the initially excited state to a low-lying Rydberg state during the relaxation of photoexcited ethylene. The measured photoelectron kinetic energy spectrum reveals wave packet motion on the valence state and shows indications that the low-lying π3s Rydberg state is indeed transiently populated via internal conversion following excitation to the ππ(∗) state, supporting the theoretical predictions.

    View details for PubMedID 26747802

  • Shapes and vorticities of superfluid helium nanodroplets SCIENCE Gomez, L. F., Ferguson, K. R., Cryan, J. P., Bacellar, C., Tanyag, R. M., Jones, C., Schorb, S., Anielski, D., Belkacem, A., Bernando, C., Boll, R., Bozek, J., Carron, S., Chen, G., Delmas, T., Englert, L., Epp, S. W., Erk, B., Foucar, L., Hartmann, R., Hexemer, A., Huth, M., Kwok, J., Leone, S. R., Ma, J. H., Maia, F. R., Malmerberg, E., Marchesini, S., Neumark, D. M., Poon, B., Prell, J., Rolles, D., Rudek, B., Rudenko, A., Seifrid, M., Siefermann, K. R., Sturm, F. P., Swiggers, M., Ullrich, J., Weise, F., Zwart, P., Bostedt, C., Gessner, O., Vilesov, A. F. 2014; 345 (6199): 906-909

    Abstract

    Helium nanodroplets are considered ideal model systems to explore quantum hydrodynamics in self-contained, isolated superfluids. However, exploring the dynamic properties of individual droplets is experimentally challenging. In this work, we used single-shot femtosecond x-ray coherent diffractive imaging to investigate the rotation of single, isolated superfluid helium-4 droplets containing ~10(8) to 10(11) atoms. The formation of quantum vortex lattices inside the droplets is confirmed by observing characteristic Bragg patterns from xenon clusters trapped in the vortex cores. The vortex densities are up to five orders of magnitude larger than those observed in bulk liquid helium. The droplets exhibit large centrifugal deformations but retain axially symmetric shapes at angular velocities well beyond the stability range of viscous classical droplets.

    View details for DOI 10.1126/science.1252395

    View details for Web of Science ID 000340524700039

  • Helium superfluidity. Shapes and vorticities of superfluid helium nanodroplets. Science Gomez, L. F., Ferguson, K. R., Cryan, J. P., Bacellar, C., Tanyag, R. M., Jones, C., Schorb, S., Anielski, D., Belkacem, A., Bernando, C., Boll, R., Bozek, J., Carron, S., Chen, G., Delmas, T., Englert, L., Epp, S. W., Erk, B., Foucar, L., Hartmann, R., Hexemer, A., Huth, M., Kwok, J., Leone, S. R., Ma, J. H., Maia, F. R., Malmerberg, E., Marchesini, S., Neumark, D. M., Poon, B., Prell, J., Rolles, D., Rudek, B., Rudenko, A., Seifrid, M., Siefermann, K. R., Sturm, F. P., Swiggers, M., Ullrich, J., Weise, F., Zwart, P., Bostedt, C., Gessner, O., Vilesov, A. F. 2014; 345 (6199): 906-909

    Abstract

    Helium nanodroplets are considered ideal model systems to explore quantum hydrodynamics in self-contained, isolated superfluids. However, exploring the dynamic properties of individual droplets is experimentally challenging. In this work, we used single-shot femtosecond x-ray coherent diffractive imaging to investigate the rotation of single, isolated superfluid helium-4 droplets containing ~10(8) to 10(11) atoms. The formation of quantum vortex lattices inside the droplets is confirmed by observing characteristic Bragg patterns from xenon clusters trapped in the vortex cores. The vortex densities are up to five orders of magnitude larger than those observed in bulk liquid helium. The droplets exhibit large centrifugal deformations but retain axially symmetric shapes at angular velocities well beyond the stability range of viscous classical droplets.

    View details for DOI 10.1126/science.1252395

    View details for PubMedID 25146284

  • Enhancement of strong-field multiple ionization in the vicinity of the conical intersection in 1,3-cyclohexadiene ring opening JOURNAL OF CHEMICAL PHYSICS Petrovic, V. S., Schorb, S., Kim, J., White, J., Cryan, J. P., Glownia, J. M., Zipp, L., Broege, D., Miyabe, S., Tao, H., Martinez, T., Bucksbaum, P. H. 2013; 139 (18)

    Abstract

    Nonradiative energy dissipation in electronically excited polyatomic molecules proceeds through conical intersections, loci of degeneracy between electronic states. We observe a marked enhancement of laser-induced double ionization in the vicinity of a conical intersection during a non-radiative transition. We measured double ionization by detecting the kinetic energy of ions released by laser-induced strong-field fragmentation during the ring-opening transition between 1,3-cyclohexadiene and 1,3,5-hexatriene. The enhancement of the double ionization correlates with the conical intersection between the HOMO and LUMO orbitals.

    View details for DOI 10.1063/1.4829766

    View details for Web of Science ID 000327712800032

    View details for PubMedID 24320276

  • Transient X-Ray Fragmentation: Probing a Prototypical Photoinduced Ring Opening PHYSICAL REVIEW LETTERS Petrovic, V. S., Siano, M., White, J. L., Berrah, N., Bostedt, C., Bozek, J. D., Broege, D., Chalfin, M., Coffee, R. N., Cryan, J., Fang, L., Farrell, J. P., Frasinski, L. J., Glownia, J. M., Guehr, M., Hoener, M., Holland, D. M., Kim, J., Marangos, J. P., Martinez, T., McFarland, B. K., Minns, R. S., Miyabe, S., Schorb, S., Sension, R. J., Spector, L. S., Squibb, R., Tao, H., Underwood, J. G., Bucksbaum, P. H. 2012; 108 (25)

    Abstract

    We report the first study of UV-induced photoisomerization probed via core ionization by an x-ray laser. We investigated x-ray ionization and fragmentation of the cyclohexadiene-hexatriene system at 850 eV during the ring opening. We find that the ion-fragmentation patterns evolve over a picosecond, reflecting a change in the state of excitation and the molecular geometry: the average kinetic energy per ion fragment and H(+)-ion count increase as the ring opens and the molecule elongates. We discuss new opportunities for molecular photophysics created by optical pump x-ray probe experiments.

    View details for DOI 10.1103/PhysRevLett.108.253006

    View details for Web of Science ID 000305569100005

    View details for PubMedID 23004597

  • Ultrafast absorption of intense x rays by nitrogen molecules JOURNAL OF CHEMICAL PHYSICS Buth, C., Liu, J., Chen, M. H., Cryan, J. P., Fang, L., Glownia, J. M., Hoener, M., Coffee, R. N., Berrah, N. 2012; 136 (21)

    Abstract

    We devise a theoretical description for the response of nitrogen molecules (N(2)) to ultrashort and intense x rays from the free electron laser Linac Coherent Light Source (LCLS). We set out from a rate-equation description for the x-ray absorption by a nitrogen atom. The equations are formulated using all one-x-ray-photon absorption cross sections and the Auger and radiative decay widths of multiply-ionized nitrogen atoms. Cross sections are obtained with a one-electron theory and decay widths are determined from ab initio computations using the Dirac-Hartree-Slater (DHS) method. We also calculate all binding and transition energies of nitrogen atoms in all charge states with the DHS method as the difference of two self-consistent field (SCF) calculations (ΔSCF method). To describe the interaction with N(2), a detailed investigation of intense x-ray-induced ionization and molecular fragmentation are carried out. As a figure of merit, we calculate ion yields and the average charge state measured in recent experiments at the LCLS. We use a series of phenomenological models of increasing sophistication to unravel the mechanisms of the interaction of x rays with N(2): a single atom, a symmetric-sharing model, and a fragmentation-matrix model are developed. The role of the formation and decay of single and double core holes, the metastable states of N(2)(2+), and molecular fragmentation are explained.

    View details for DOI 10.1063/1.4722756

    View details for Web of Science ID 000305090900028

    View details for PubMedID 22697546

  • Ensemble of Linear Molecules in Nondispersing Rotational Quantum States: A Molecular Stopwatch PHYSICAL REVIEW X Cryan, J. P., Glownia, J. M., Broege, D. W., Ma, Y., Bucksbaum, P. H. 2011; 1 (1)
  • Auger Electron Angular Distribution of Double Core-Hole States in the Molecular Reference Frame PHYSICAL REVIEW LETTERS Cryan, J. P., Glownia, J. M., Andreasson, J., Belkacem, A., Berrah, N., Blaga, C. I., Bostedt, C., Bozek, J., Buth, C., DiMauro, L. F., Fang, L., Gessner, O., Guehr, M., Hajdu, J., Hertlein, M. P., Hoener, M., Kornilov, O., Marangos, J. P., March, A. M., McFarland, B. K., Merdji, H., Petrovic, V. S., Raman, C., Ray, D., Reis, D., Tarantelli, F., Trigo, M., WHITE, J. L., White, W., Young, L., Bucksbaum, P. H., Coffee, R. N. 2010; 105 (8)

    Abstract

    The Linac Coherent Light Source free electron laser is a source of high brightness x rays, 2×10(11) photons in a ∼5 fs pulse, that can be focused to produce double core vacancies through rapid sequential ionization. This enables double core vacancy Auger electron spectroscopy, an entirely new way to study femtosecond chemical dynamics with Auger electrons that probe the local valence structure of molecules near a specific atomic core. Using 1.1 keV photons for sequential x-ray ionization of impulsively aligned molecular nitrogen, we observed a rich single-site double core vacancy Auger electron spectrum near 413 eV, in good agreement with ab initio calculations, and we measured the corresponding Auger electron angle dependence in the molecular frame.

    View details for DOI 10.1103/PhysRevLett.105.083004

    View details for Web of Science ID 000281072100003

    View details for PubMedID 20868096

  • Field-free alignment in repetitively kicked nitrogen gas PHYSICAL REVIEW A Cryan, J. P., Bucksbaum, P. H., Coffee, R. N. 2009; 80 (6)