Publications

  • Liu et al., "Rehybridization dynamics into the pericyclic minimum of an electrocyclic reaction imaged in real-time." Nat. Commun. 14, 2795 (2023). In this study provides, we used a combination of megaelectronvolt ultrafast electron diffraction to reveal new mechanistic insights into electrocyclic reactions. These reactions are characterized by the simultaneous formation and dissociation of multiple bonds and by their stereospecificity, the ability to chemically lock specific reactant stereoconfigurations in the product. The results show that the stereospecificity is achieved by the multiple bond reformation steps not happening exactly at the same time.
  • Reinhard et al., "Ferricyanide photo-aquation pathway revealed by combined femtosecond Kβ main line and valence-to-core x-ray emission spectroscopy." Nat. Commun. 14, 2443 (2023). In this study we utilized fs Fe Kβ main line and valence to core X-ray emission spectroscopy, along with x-ray solution scattering, to investigate the photo-aquation reaction of ferricyanide under UV excitation. By analyzing both the Fe Kβ main line and the valence-to-core regions, we were able to identify short-lived intermediates crucial for understanding the reaction mechanism. In the proposed reaction process, the photoexcited ligand-to-metal charge transfer excited state undergoes sub-ps deactivation through dissociative metal-centered excited states, resulting in the formation of a penta-coordinate intermediate. This intermediate decays within 5 ps either by rebinding the dissociated cyanide or via uptake of a water molecule. The methodology employed in this study holds broad applicability for studying reactions in more intricate systems, including heme proteins.
  • van Driel et al., “The epix10k 2-megapixel hard X-ray detector at LCLS”. J. Synchrotron Radiat. 27, 608-615 (2020)
    Here the first measurements on the new ePix10k detector are presented and the performance under typical XFEL conditions evaluated during an LCLS X-ray diffuse scattering experiment measuring the 9.5 keV X-ray photons scattered from a thin liquid jet.
  • Kunnus et al., “Vibrational wavepacket dynamics in Fe carbene photosensitizer determined with femtosecond X-ray emission and scattering“. Nat. Comm. 11, 634 (2020)
    Here we investigate the photoinduced dynamics of the [Fe(bmip)2]2+ photosensitizer, where bmip = 2,6-bis(3-methyl-imidazole-1-ylidine)-pyridine, with simultaneous femtosecond-resolution Fe Kα and Kβ X-ray emission spectroscopy (XES) and X-ray solution scattering (XSS). This measurement shows temporal oscillations in the XES and XSS difference signals with the same 278 fs period oscillation originating from an Fe-ligand stretching vibrational wavepacket on a triplet metal-centered (3MC) excited state surface. This 3MC state is populated with a 110 fs time constant by 40% of the excited molecules while the rest relax to a 3MLCT excited state. The sensitivity of the Kα XES to molecular structure results from a 0.7% average Fe-ligand bond length shift between the 1 s and 2p core-ionized states surfaces.
  • Ledbetter et al., “Excited state charge distribution and bond expansion of ferrous complexes observed with femtosecond valence-to-core x-ray emission spectroscopy”. J. Chem. Phys. 152, 074203 (2020)
    Here we demonstrate the use of the high-sensitive but low yield valence-to-core x-ray emission spectroscopy (VtC XES) to study geometric and electronic structural changes induced by photoexcitation in the fs time domain. Time-resolved VtC XES on a series of ferrous complexes [Fe(CN)2n(2, 2′-bipyridine)3−n]−2n+2, n = 1, 2, 3, are compared with ground state DFT calculations revealing signatures of excited state bond length and oxidation state changes. An oxidation state change associated with a metal-to-ligand charge transfer state with a lifetime of less than 100 fs is observed, as well as bond length changes associated with metal-centered excited states with lifetimes of 13 ps and 250 ps.
  • Alonso-Mori et al., “Femtosecond electronic structure response to high intensity XFEL pulses probed by iron X-ray emission spectroscopy”. Sci. Rep. 10 (1), 1-7 (2020)
    This paper reports the time-resolved femtosecond evolution of the K-shell X-ray emission spectra of iron during high intensity illumination of X-rays in the micron-sized focused LCLS beam. 
  • Nunes et al., "Liquid-phase Mega-electron-volt ultrafast electron diffraction", Struct. Dyn., 7, 024301 (2020)
    This instrument paper describes the liquid phase ultrafast electron diffraction endstation and results from static investigations of the structure of water.
  • Yang et al., "Simultaneous observation of nuclear and electronic dynamics by ultrafast electron diffraction", Science, 368, 885 (2020).
    This paper showcases the sensitivity of electron diffraction to electronic structure changes in addition to its sensitivity to structural dynamics.
  • Wolf and Gühr, "Photochemical Pathways in Nucleobases measured with an X-ray FEL", ‎Philos. Trans. Royal Soc. A, 377, 20170473 (2019).
    This is a review paper for time-resolved gas phase spectroscopy with soft X-rays for photochemical dynamcis.

2017

2016

  • van Driel, et al. "Atomistic characterization of the active-site solvation dynamics of a model photocatalyst". Nature communications 7, 13678 (2016)
    This paper reports the investigation of the structural and solvation dynamics following excitation of a model photocatalytic molecular system [Ir2(dimen)4]2+, where dimen is para-diisocyanomenthane. It provides evidence for the coordination of the iridium atoms by the acetonitrile solvent and demonstrates the viability of using diffuse X-ray scattering at free-electron laser sources for studying the dynamics of photocatalysis.
  • Alonso-Mori et al. “Towards characterization of photo-excited electron transfer and catalysis in natural and artificial systems using XFELs” Faraday discussions 194, 621-638 (2016)
    This paper describes the methodology we developed for simultaneously collecting X-ray diffraction data and X-ray emission spectra, using an energy dispersive spectrometer, at ambient conditions. It includes a review of the studies up to 2016 of the room temperature structure and intermediate states of the photosynthetic water oxidizing metalloprotein photosystem II. 

​2015

​Older

  • Alonso-Mori et al., “Energy-dispersive X-ray emission spectroscopy using an X-ray free-electron laser in a shot-by-shot mode”. PNAS, 109, 47 (2012)
    Reporting the first fs X-ray emission spectroscopy measurement LCLS using redox-active Mn complexes. The spectra were found in agreement with undamaged spectra collected at low dose using synchrotron radiation. These results demonstrate that the intact electronic structure of redox active transition metals can be measured at LCLS, addressing the question whether the “probe-before-destroy” approach, previously demonstrated for atomic structure determination, could be extended to probe the local electronic structure by X-ray spectroscopy, which occurs in faster time-scales.
  • Alonso-Mori et al., “A multi-crystal wavelength dispersive x-ray spectrometer”. Rev. Sci. Inst. 83 (7), 073114 (2012)
    This paper describes the LCLS 16 crystal X-ray emission spectrometer based on the energy dispersive von Hamos geometry. This spectrometer and/or modifications of it are regularly used at LCLS in the liquid jet standard configuration for solution phase chemistry and in the XRD/XES biochemistry experiments.