James P. Cryan

All Publications

• Attosecond delays in X-ray molecular ionization. Nature Driver, T., Mountney, M., Wang, J., Ortmann, L., Al-Haddad, A., Berrah, N., Bostedt, C., Champenois, E. G., DiMauro, L. F., Duris, J., Garratt, D., Glownia, J. M., Guo, Z., Haxton, D., Isele, E., Ivanov, I., Ji, J., Kamalov, A., Li, S., Lin, M. F., Marangos, J. P., Obaid, R., O'Neal, J. T., Rosenberger, P., Shivaram, N. H., Wang, A. L., Walter, P., Wolf, T. J., Wörner, H. J., Zhang, Z., Bucksbaum, P. H., Kling, M. F., Landsman, A. S., Lucchese, R. R., Emmanouilidou, A., Marinelli, A., Cryan, J. P. 2024; 632 (8026): 762-767

  Abstract

  The photoelectric effect is not truly instantaneous but exhibits attosecond delays that can reveal complex molecular dynamics1-7. Sub-femtosecond-duration light pulses provide the requisite tools to resolve the dynamics of photoionization8-12. Accordingly, the past decade has produced a large volume of work on photoionization delays following single-photon absorption of an extreme ultraviolet photon. However, the measurement of time-resolved core-level photoionization remained out of reach. The required X-ray photon energies needed for core-level photoionization were not available with attosecond tabletop sources. Here we report measurements of the X-ray photoemission delay of core-level electrons, with unexpectedly large delays, ranging up to 700 as in NO near the oxygen K-shell threshold. These measurements exploit attosecond soft X-ray pulses from a free-electron laser to scan across the entire region near the K-shell threshold. Furthermore, we find that the delay spectrum is richly modulated, suggesting several contributions, including transient trapping of the photoelectron owing to shape resonances, collisions with the Auger-Meitner electron that is emitted in the rapid non-radiative relaxation of the molecule and multi-electron scattering effects. The results demonstrate how X-ray attosecond experiments, supported by comprehensive theoretical modelling, can unravel the complex correlated dynamics of core-level photoionization.

  View details for DOI 10.1038/s41586-024-07771-9

  View details for PubMedID 39169246

  View details for PubMedCentralID 7399650

• Terawatt-scale attosecond X-ray pulses from a cascaded superradiant free-electron laser NATURE PHOTONICS Franz, P., Li, S., Driver, T., Robles, R. R., Cesar, D., Isele, E., Guo, Z., Wang, J., Duris, J. P., Larsen, K., Glownia, J. M., Cheng, X., Hoffmann, M. C., Li, X., Lin, M., Kamalov, A., Obaid, R., Summers, A., Sudar, N., Thierstein, E., Zhang, Z., Kling, M. F., Huang, Z., Cryan, J. P., Marinelli, A. 2024

  View details for DOI 10.1038/s41566-024-01427-w

  View details for Web of Science ID 001220935700001

• Experimental demonstration of attosecond pump-probe spectroscopy with an X-ray free-electron laser NATURE PHOTONICS Guo, Z., Driver, T., Beauvarlet, S., Cesar, D., Duris, J., Franz, P. L., Alexander, O., Bohler, D., Bostedt, C., Averbukh, V., Cheng, X., Dimauro, L. F., Doumy, G., Forbes, R., Gessner, O., Glownia, J. M., Isele, E., Kamalov, A., Larsen, K. A., Li, S., Li, X., Lin, M., Mccracken, G. A., Obaid, R., O'Neal, J. T., Robles, R. R., Rolles, D., Ruberti, M., Rudenko, A., Slaughter, D. S., Sudar, N. S., Thierstein, E., Tuthill, D., Ueda, K., Wang, E., Wang, A. L., Wang, J., Weber, T., Wolf, T. A., Young, L., Zhang, Z., Bucksbaum, P. H., Marangos, J. P., Kling, M. F., Huang, Z., Walter, P., Inhester, L., Berrah, N., Cryan, J. P., Marinelli, A. 2024

  View details for DOI 10.1038/s41566-024-01419-w

  View details for Web of Science ID 001200371400001

• Photon energy-resolved velocity map imaging from spectral domain ghost imaging NEW JOURNAL OF PHYSICS Wang, J., Driver, T., Allum, F., Papadopoulou, C. C., Passow, C., Brenner, G., Li, S., Duesterer, S., Tul Noor, A., Kumar, S., Bucksbaum, P. H., Erk, B., Forbes, R., Cryan, J. P. 2023; 25 (3)

  View details for DOI 10.1088/1367-2630/acc201

  View details for Web of Science ID 000956244500001

• Attosecond coherent electron motion in Auger-Meitner decay. Science (New York, N.Y.) Li, S., Driver, T., Rosenberger, P., Champenois, E. G., Duris, J., Al-Haddad, A., Averbukh, V., Barnard, J. C., Berrah, N., Bostedt, C., Bucksbaum, P. H., Coffee, R. N., DiMauro, L. F., Fang, L., Garratt, D., Gatton, A., Guo, Z., Hartmann, G., Haxton, D., Helml, W., Huang, Z., LaForge, A. C., Kamalov, A., 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., Wang, A. L., Wolf, T. J., Zhang, Z., Kling, M. F., Marinelli, A., Cryan, J. P. 1800: eabj2096

  Abstract

  [Figure: see text].

  View details for DOI 10.1126/science.abj2096

  View details for PubMedID 34990213

• The development of attosecond XFELs for understanding ultrafast electron motion ADVANCES IN ATOMIC, MOLECULAR, AND OPTICAL PHYSICS, VOL. 71 Cryan, J. P., Driver, T., Duris, J., Guo, Z., Li, S., O'Neal, J. T., Marinelli, A., DiMauro, L. F., Perrin, H., Yelin, S. F. 2022; 71: 1-64

  View details for DOI 10.1016/bs.aamop.2022.05.001

  View details for Web of Science ID 000877680100002

• Controllable X-Ray Pulse Trains from Enhanced Self-Amplified Spontaneous Emission. Physical review letters Duris, J. P., MacArthur, J. P., Glownia, J. M., Li, S., Vetter, S., Miahnahri, A., Coffee, R., Hering, P., Fry, A., Welch, M. E., Lutman, A., Decker, F., Bohler, D., Mock, J. A., Xu, C., Gumerlock, K., May, J. E., Cedillos, A., Kraft, E., Carrasco, M. A., Smith, B. E., Chieffo, L. R., Xu, J. Z., Cryan, J. P., Huang, Z., Zholents, A., Marinelli, A. 2021; 126 (10): 104802

  Abstract

  We report the demonstration of optical compression of an electron beam and the production of controllable trains of femtosecond, soft x-ray pulses with the Linac Coherent Light Source (LCLS) free-electron laser (FEL). This is achieved by enhanced self-amplified spontaneous emission with a 2mum laser and a dechirper device. Optical compression was achieved by modulating the energy of an electron beam with the laser and then compressing with a chicane, resulting in high current spikes on the beam which we observe to lase. A dechirper was then used to selectively control the lasing region of the electron beam. Field autocorrelation measurements indicate a train of pulses, and we find that the number of pulses within the train can be controlled (from 1 to 5 pulses) by varying the dechirper position and undulator taper. These results are a step toward attosecond spectroscopy with x-ray FELs as well as future FEL schemes relying on optical compression of an electron beam.

  View details for DOI 10.1103/PhysRevLett.126.104802

  View details for PubMedID 33784160

• Electron correlation effects in attosecond photoionization of CO2 PHYSICAL REVIEW A Kamalov, A., Wang, A. L., Bucksbaum, P. H., Haxton, D. J., Cryan, J. P. 2020; 102 (2)

  View details for DOI 10.1103/PhysRevA.102.023118

  View details for Web of Science ID 000565703000005

• 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., Obaid, R., Al-Haddad, A., Barnard, J., Berrah, N., Coffee, R., Duris, J., Galinis, G., Garratt, D., Glownia, J. M., Haxton, D., Ho, P., Li, S., Li, X., MacArthur, J., Marangos, J. P., Natan, A., Shivaram, N., Slaughter, D. S., Walter, P., Wandel, S., Young, L., Bostedt, C., Bucksbaum, P. H., Picón, A., Marinelli, A., 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

• 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-+

  View details for DOI 10.1038/s41566-019-0549-5

  View details for Web of Science ID 000504727600007

• 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)

  View details for DOI 10.1098/rsta.2018.0386

  View details for Web of Science ID 000465499800015

• 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

• Tracking dissociation pathways of nitrobenzene via mega-electron-volt ultrafast electron diffraction JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS Hegazy, K., Bucksbaum, P., Centurion, M., Cryan, J., Li, R., Lin, M., Moore, B., Nunes, P., Shen, X., Weathersby, S., Yang, J., Wang, X., Wolf, T. 2024; 57 (19)

  View details for DOI 10.1088/1361-6455/ad7431

  View details for Web of Science ID 001306576300001

• Attosecond impulsive stimulated X-ray Raman scattering in liquid water. Science advances Alexander, O., Egun, F., Rego, L., Gutierrez, A. M., Garratt, D., Cardenes, G. A., Nogueira, J. J., Lee, J. P., Zhao, K., Wang, R. P., Ayuso, D., Barnard, J. C., Beauvarlet, S., Bucksbaum, P. H., Cesar, D., Coffee, R., Duris, J., Frasinski, L. J., Huse, N., Kowalczyk, K. M., Larsen, K. A., Matthews, M., Mukamel, S., O'Neal, J. T., Penfold, T., Thierstein, E., Tisch, J. W., Turner, J. R., Vogwell, J., Driver, T., Berrah, N., Lin, M. F., Dakovski, G. L., Moeller, S. P., Cryan, J. P., Marinelli, A., Picón, A., Marangos, J. P. 2024; 10 (39): eadp0841

  Abstract

  We report the measurement of impulsive stimulated x-ray Raman scattering in neutral liquid water. An attosecond pulse drives the excitations of an electronic wavepacket in water molecules. The process comprises two steps: a transition to core-excited states near the oxygen atoms accompanied by transition to valence-excited states. Thus, the wavepacket is impulsively created at a specific atomic site within a few hundred attoseconds through a nonlinear interaction between the water and the x-ray pulse. We observe this nonlinear signature in an intensity-dependent Stokes Raman sideband at 526 eV. Our measurements are supported by our state-of-the-art calculations based on the polarization response of water dimers in bulk solvation and propagation of attosecond x-ray pulses at liquid density.

  View details for DOI 10.1126/sciadv.adp0841

  View details for PubMedID 39321305

• Efficient prediction of attosecond two-colour pulses from an X-ray free-electron laser with machine learning. Scientific reports Alaa El-Din, K. K., Alexander, O. G., Frasinski, L. J., Mintert, F., Guo, Z., Duris, J., Zhang, Z., Cesar, D. B., Franz, P., Driver, T., Walter, P., Cryan, J. P., Marinelli, A., Marangos, J. P., Mukherjee, R. 2024; 14 (1): 7267

  Abstract

  X-ray free-electron lasers are sources of coherent, high-intensity X-rays with numerous applications in ultra-fast measurements and dynamic structural imaging. Due to the stochastic nature of the self-amplified spontaneous emission process and the difficulty in controlling injection of electrons, output pulses exhibit significant noise and limited temporal coherence. Standard measurement techniques used for characterizing two-coloured X-ray pulses are challenging, as they are either invasive or diagnostically expensive. In this work, we employ machine learning methods such as neural networks and decision trees to predict the central photon energies of pairs of attosecond fundamental and second harmonic pulses using parameters that are easily recorded at the high-repetition rate of a single shot. Using real experimental data, we apply a detailed feature analysis on the input parameters while optimizing the training time of the machine learning methods. Our predictive models are able to make predictions of central photon energy for one of the pulses without measuring the other pulse, thereby leveraging the use of the spectrometer without having to extend its detection window. We anticipate applications in X-ray spectroscopy using XFELs, such as in time-resolved X-ray absorption and photoemission spectroscopy, where improved measurement of input spectra will lead to better experimental outcomes.

  View details for DOI 10.1038/s41598-024-56782-z

  View details for PubMedID 38538610

  View details for PubMedCentralID 4038304

• Attosecond-pump attosecond-probe x-ray spectroscopy of liquid water. Science (New York, N.Y.) Li, S., Lu, L., Bhattacharyya, S., Pearce, C., Li, K., Nienhuis, E. T., Doumy, G., Schaller, R. D., Moeller, S., Lin, M. F., Dakovski, G., Hoffman, D. J., Garratt, D., Larsen, K. A., Koralek, J. D., Hampton, C. Y., Cesar, D., Duris, J., Zhang, Z., Sudar, N., Cryan, J. P., Marinelli, A., Li, X., Inhester, L., Santra, R., Young, L. 2024: eadn6059

  Abstract

  Attosecond-pump/attosecond-probe experiments have long been sought as the most straightforward method to observe electron dynamics in real time. Although numerous successes have been achieved with overlapped near infrared femtosecond and extreme ultraviolet attosecond pulses combined with theory, true attosecond-pump/attosecond-probe experiments have been limited. We used a synchronized attosecond x-ray pulse pair from an x-ray free electron laser to study the electronic response to valence ionization in liquid water via all x-ray attosecond transient absorption spectroscopy (AX-ATAS). Our analysis showed that the AX-ATAS response is confined to the subfemtosecond timescale, eliminating any hydrogen atom motion and demonstrating experimentally that the 1b1 splitting in the x-ray emission spectrum is related to dynamics and is not evidence for two structural motifs in ambient liquid water.

  View details for DOI 10.1126/science.adn6059

  View details for PubMedID 38359104

• Applying Bayesian inference and deterministic anisotropy to retrieve the molecular structure ÷Ψ(<bold>R</bold>)÷<SUP>2</SUP> distribution from gas-phase diffraction experiments COMMUNICATIONS PHYSICS Hegazy, K., Makhija, V., Bucksbaum, P., Corbett, J., Cryan, J., Hartmann, N., Ilchen, M., Jobe, K., Li, R., Makasyuk, I., Shen, X., Wang, X., Weathersby, S., Yang, J., Coffee, R. 2023; 6 (1)

  View details for DOI 10.1038/s42005-023-01420-9

  View details for Web of Science ID 001123559000001

• Compact single-shot soft X-ray photon spectrometer for free-electron laser diagnostics OPTICS EXPRESS Larsen, K. A., Borne, K., Obaid, R., Kamalov, A., Liu, Y., Cheng, X., James, J., Driver, T., Li, K., Liu, Y., Sakdinawat, A., David, C., Wolf, T. A., Cryan, J. P., Walter, P., Lin, M. 2023; 31 (22): 35822-35834

  Abstract

  The photon spectrum from free-electron laser (FEL) light sources offers valuable information in time-resolved experiments and machine optimization in the spectral and temporal domains. We have developed a compact single-shot photon spectrometer to diagnose soft X-ray spectra. The spectrometer consists of an array of off-axis Fresnel zone plates (FZP) that act as transmission-imaging gratings, a Ce:YAG scintillator, and a microscope objective to image the scintillation target onto a two-dimensional imaging detector. This spectrometer operates in segmented energy ranges which covers tens of electronvolts for each absorption edge associated with several atomic constituents: carbon, nitrogen, oxygen, and neon. The spectrometer's performance is demonstrated at a repetition rate of 120 Hz, but our detection scheme can be easily extended to 200 kHz spectral collection by employing a fast complementary metal oxide semiconductor (CMOS) line-scan camera to detect the light from the scintillator. This compact photon spectrometer provides an opportunity for monitoring the spectrum downstream of an endstation in a limited space environment with sub-electronvolt energy resolution.

  View details for DOI 10.1364/OE.502105

  View details for Web of Science ID 001106418000001

  View details for PubMedID 38017746

• Femtosecond Electronic and Hydrogen Structural Dynamics in Ammonia Imaged with Ultrafast Electron Diffraction. Physical review letters Champenois, E. G., List, N. H., Ware, M., Britton, M., Bucksbaum, P. H., Cheng, X., Centurion, M., Cryan, J. P., Forbes, R., Gabalski, I., Hegazy, K., Hoffmann, M. C., Howard, A. J., Ji, F., Lin, M. F., Nunes, J. P., Shen, X., Yang, J., Wang, X., Martinez, T. J., Wolf, T. J. 2023; 131 (14): 143001

  Abstract

  Directly imaging structural dynamics involving hydrogen atoms by ultrafast diffraction methods is complicated by their low scattering cross sections. Here we demonstrate that megaelectronvolt ultrafast electron diffraction is sufficiently sensitive to follow hydrogen dynamics in isolated molecules. In a study of the photodissociation of gas phase ammonia, we simultaneously observe signatures of the nuclear and corresponding electronic structure changes resulting from the dissociation dynamics in the time-dependent diffraction. Both assignments are confirmed by ab initio simulations of the photochemical dynamics and the resulting diffraction observable. While the temporal resolution of the experiment is insufficient to resolve the dissociation in time, our results represent an important step towards the observation of proton dynamics in real space and time.

  View details for DOI 10.1103/PhysRevLett.131.143001

  View details for PubMedID 37862660

• Time-Resolved X-ray Photoelectron Spectroscopy: Ultrafast Dynamics in CS2 Probed at the S 2p Edge. The journal of physical chemistry letters Gabalski, I., Allum, F., Seidu, I., Britton, M., Brenner, G., Bromberger, H., Brouard, M., Bucksbaum, P. H., Burt, M., Cryan, J. P., Driver, T., Ekanayake, N., Erk, B., Garg, D., Gougoula, E., Heathcote, D., Hockett, P., Holland, D. M., Howard, A. J., Kumar, S., Lee, J. W., Li, S., McManus, J., Mikosch, J., Milesevic, D., Minns, R. S., Neville, S., Papadopoulou, C. C., Passow, C., Razmus, W. O., Röder, A., Rouzée, A., Simao, A., Unwin, J., Vallance, C., Walmsley, T., Wang, J., Rolles, D., Stolow, A., Schuurman, M. S., Forbes, R. 2023: 7126-7133

  Abstract

  Recent developments in X-ray free-electron lasers have enabled a novel site-selective probe of coupled nuclear and electronic dynamics in photoexcited molecules, time-resolved X-ray photoelectron spectroscopy (TRXPS). We present results from a joint experimental and theoretical TRXPS study of the well-characterized ultraviolet photodissociation of CS2, a prototypical system for understanding non-adiabatic dynamics. These results demonstrate that the sulfur 2p binding energy is sensitive to changes in the nuclear structure following photoexcitation, which ultimately leads to dissociation into CS and S photoproducts. We are able to assign the main X-ray spectroscopic features to the CS and S products via comparison to a first-principles determination of the TRXPS based on ab initio multiple-spawning simulations. Our results demonstrate the use of TRXPS as a local probe of complex ultrafast photodissociation dynamics involving multimodal vibrational coupling, nonradiative transitions between electronic states, and multiple final product channels.

  View details for DOI 10.1021/acs.jpclett.3c01447

  View details for PubMedID 37534743

• Rehybridization dynamics into the pericyclic minimum of an electrocyclic reaction imaged in real-time. Nature communications Liu, Y., Sanchez, D. M., Ware, M. R., Champenois, E. G., Yang, J., Nunes, J. P., Attar, A., Centurion, M., Cryan, J. P., Forbes, R., Hegazy, K., Hoffmann, M. C., Ji, F., Lin, M., Luo, D., Saha, S. K., Shen, X., Wang, X. J., Martinez, T. J., Wolf, T. J. 2023; 14 (1): 2795

  Abstract

  Electrocyclic reactions are characterized by the concerted formation and cleavage of both sigma and pi bonds through a cyclic structure. This structure is known as a pericyclic transition state for thermal reactions and a pericyclic minimum in the excited state for photochemical reactions. However, the structure of the pericyclic geometry has yet to be observed experimentally. We use a combination of ultrafast electron diffraction and excited state wavepacket simulations to image structural dynamics through the pericyclic minimum of a photochemical electrocyclic ring-opening reaction in the molecule alpha-terpinene. The structural motion into the pericyclic minimum is dominated by rehybridization of two carbon atoms, which is required for the transformation from two to three conjugated pi bonds. The sigma bond dissociation largely happens after internal conversion from the pericyclic minimum to the electronic ground state. These findings may be transferrable to electrocyclic reactions in general.

  View details for DOI 10.1038/s41467-023-38513-6

  View details for PubMedID 37202402

• Effect of the shot-to-shot variation on charge migration induced by sub-fs x-ray free-electron laser pulses PHYSICAL REVIEW RESEARCH Grell, G., Guo, Z., Driver, T., Decleva, P., Plesiat, E., Picon, A., Gonzalez-Vazquez, J., Walter, P., Marangos, J. P., Cryan, J. P., Marinelli, A., Palacios, A., Martin, F. 2023; 5 (2)

  View details for DOI 10.1103/PhysRevResearch.5.023092

  View details for Web of Science ID 000995777100002

• The time-resolved atomic, molecular and optical science instrument at the Linac Coherent Light Source. Journal of synchrotron radiation Walter, P., Osipov, T., Lin, M. F., Cryan, J., Driver, T., Kamalov, A., Marinelli, A., Robinson, J., Seaberg, M. H., Wolf, T. J., Aldrich, J., Brown, N., Champenois, E. G., Cheng, X., Cocco, D., Conder, A., Curiel, I., Egger, A., Glownia, J. M., Heimann, P., Holmes, M., Johnson, T., Lee, L., Li, X., Moeller, S., Morton, D. S., Ng, M. L., Ninh, K., O'Neal, J. T., Obaid, R., Pai, A., Schlotter, W., Shepard, J., Shivaram, N., Stefan, P., Van, X., Wang, A. L., Wang, H., Yin, J., Yunus, S., Fritz, D., James, J., Castagna, J. C. 2022; 29 (Pt 4): 957-968

  Abstract

  The newly constructed time-resolved atomic, molecular and optical science instrument (TMO) is configured to take full advantage of both linear accelerators at SLAC National Accelerator Laboratory, the copper accelerator operating at a repetition rate of 120 Hz providing high per-pulse energy as well as the superconducting accelerator operating at a repetition rate of about 1 MHz providing high average intensity. Both accelerators power a soft X-ray free-electron laser with the new variable-gap undulator section. With this flexible light source, TMO supports many experimental techniques not previously available at LCLS and will have two X-ray beam focus spots in line. Thereby, TMO supports atomic, molecular and optical, strong-field and nonlinear science and will also host a designated new dynamic reaction microscope with a sub-micrometer X-ray focus spot. The flexible instrument design is optimized for studying ultrafast electronic and molecular phenomena and can take full advantage of the sub-femtosecond soft X-ray pulse generation program.

  View details for DOI 10.1107/S1600577522004283

  View details for PubMedID 35787561

• Characterization of single-shot attosecond pulses with angular streaking photoelectron spectra PHYSICAL REVIEW A Zhao, X., Li, S., Driver, T., Van-Hung Hoang, Anh-Thu Le, Cryan, J. P., Marinelli, A., Lin, C. D. 2022; 105 (1)

  View details for DOI 10.1103/PhysRevA.105.013111

  View details for Web of Science ID 000747560000006

• Role of nuclear-electronic coupling in attosecond photoionization of H-2 PHYSICAL REVIEW A Wang, A. L., Serov, V. V., Kamalov, A., Bucksbaum, P. H., Kheifets, A., Cryan, J. P. 2021; 104 (6)

  View details for DOI 10.1103/PhysRevA.104.063119

  View details for Web of Science ID 000737281100001

• Time-resolved pump-probe spectroscopy with spectral domain ghost imaging. Faraday discussions Li, S., Driver, T., Alexander, O., Cooper, B., Garratt, D., Marinelli, A., Cryan, J. P., Marangos, J. P. 2021

  Abstract

  An atomic-level picture of molecular and bulk processes, such as chemical bonding and charge transfer, necessitates an understanding of the dynamical evolution of these systems. On the ultrafast timescales associated with nuclear and electronic motion, the temporal behaviour of a system is often interrogated in a 'pump-probe' scheme. Here, an initial 'pump' pulse triggers dynamics through photoexcitation, and after a carefully controlled delay a 'probe' pulse initiates projection of the instantaneous state of the evolving system onto an informative measurable quantity, such as electron binding energy. In this paper, we apply spectral ghost imaging to a pump-probe time-resolved experiment at an X-ray free-electron laser (XFEL) facility, where the observable is spectral absorption in the X-ray regime. By exploiting the correlation present in the shot-to-shot fluctuations in the incoming X-ray pulses and measured electron kinetic energies, we show that spectral ghost imaging can be applied to time-resolved pump-probe measurements. In the experiment presented, interpretation of the measurement is simplified because spectral ghost imaging separates the overlapping contributions to the photoelectron spectrum from the pump and probe pulse.

  View details for DOI 10.1039/d0fd00122h

  View details for PubMedID 33625412

• Transient resonant Auger-Meitner spectra of photoexcited thymine. Faraday discussions Wolf, T. J., Paul, A. C., Folkestad, S. D., Myhre, R. H., Cryan, J. P., Berrah, N., Bucksbaum, P. H., Coriani, S., Coslovich, G., Feifel, R., Martinez, T. J., Moeller, S. P., Mucke, M., Obaid, R., Plekan, O., Squibb, R. J., Koch, H., Guhr, M. 2021

  Abstract

  We present the first investigation of excited state dynamics by resonant Auger-Meitner spectroscopy (also known as resonant Auger spectroscopy) using the nucleobase thymine as an example. Thymine is photoexcited in the UV and probed with X-ray photon energies at and below the oxygen K-edge. After initial photoexcitation to a pipi* excited state, thymine is known to undergo internal conversion to an npi* excited state with a strong resonance at the oxygen K-edge, red-shifted from the ground state pi* resonances of thymine (see our previous study Wolf, et al., Nat. Commun., 2017, 8, 29). We resolve and compare the Auger-Meitner electron spectra associated both with the excited state and ground state resonances, and distinguish participator and spectator decay contributions. Furthermore, we observe simultaneously with the decay of the npi* state signatures the appearance of additional resonant Auger-Meitner contributions at photon energies between the npi* state and the ground state resonances. We assign these contributions to population transfer from the npi* state to a pipi* triplet state via intersystem crossing on the picosecond timescale based on simulations of the X-ray absorption spectra in the vibrationally hot triplet state. Moreover, we identify signatures from the initially excited pipi* singlet state which we have not observed in our previous study.

  View details for DOI 10.1039/d0fd00112k

  View details for PubMedID 33566045

• 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

• Inner Valence Hole Migration in Isopropanol Alexander, O., Barillot, T., Cooper, B., Driver, T., Garratt, D., Li, S., Marinelli, A., Cryan, J. P., Marangos, J. P., LR25 Collaboration, IEEE IEEE. 2021

  View details for DOI 10.1109/CLEO/Europe-EQEC52157.2021.9542202

  View details for Web of Science ID 000728078300580

• Arrival Time Monitor for Sub-10 fs Soft X-ray and 800 nm Optical Pulses Muhammad, I., Frimpong, B., Daafour, J., Xu, X., Walter, P., Wolf, T. A., Cryan, J. P., Glownia, J. M., Robinson, J. S., Droste, S., Coslovich, G., IEEE IEEE. 2021

  View details for Web of Science ID 000831479802212

• 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)

  View details for DOI 10.1103/PhysRevX.10.011065

  View details for Web of Science ID 000519993700001

• 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

• 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

• 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)

  View details for DOI 10.1098/rsta.2017.0477

  View details for Web of Science ID 000465499800010

• 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

• 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

  View details for Web of Science ID 000482226301273

• Imaging CF3I conical intersection and photodissociation dynamics with ultrafast electron diffraction. Science (New York, N.Y.) Yang, J., Zhu, X., Wolf, T. J., Li, Z., Nunes, J. P., 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

  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 DOI 10.1126/science.aat0049

  View details for PubMedID 29976821

• 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

• 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)

  View details for DOI 10.1103/PhysRevA.95.023412

  View details for Web of Science ID 000394366300004

• 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

• 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., 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 DOI 10.1063/1.4939220

  View details for PubMedID 26747802

• 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

• 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)

  View details for DOI 10.1103/PhysRevX.1.011002

  View details for Web of Science ID 000310504700002

• 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)

  View details for DOI 10.1103/PhysRevA.80.063412

  View details for Web of Science ID 000273233800111