Speaker
Description
Ultrafast X-ray spectroscopic investigations and molecular dynamics are now achievable with short X-ray pulses produced by laboratory table-top high-order harmonics. Those X-rays probe transitions from localized inner shells on specific atomic sites in the molecules to valence orbitals, conveying new information about photochemical transformations. The interpretations of these spectra involve a new regime of core-to-valence X-ray probing that depends on energy shifts due to the surrounding electronic densities, spin-coupling effects, energy shifts due to bond elongation with vibrational excitation and bond angles. Coherent vibrational superpositions reveal different slopes of inner shell potentials with bond extension and Fermi resonance coupling in the X-ray. Precision measurements of bond length changes can be as small as 0.0001 Angstrom. Real time observations of Jahn-Teller distortion and passage through conical intersections are achieved. Open shell radicals have characteristic features of singly occupied orbitals and energetic shifts upon bond cleavage, and spin splittings, which can be viewed from the localized atomic perspective. Corresponding theory work by collaborators provides a powerful assessment of the dynamics through X-ray spectroscopic investigations. Progress in revealing the full potential of time-resolved X-ray spectroscopy for the investigation of numerous novel features in molecular photochemistry is discussed.
J. H. Ou, D. Hait, P. Rupprecht, J. E. Beetar, T. J. Martínez, S. R. Leone, “Attosecond probing of coherent vibrational dynamics in CBr4,” J. Phys. Chem. A 128, 9208–9217 (2024).
A. D. Ross, D. Hait, V. Scutelnic, D. M. Neumark, M. Head-Gordon, S. R. Leone, “Measurement of coherent vibrational dynamics with X-ray transient absorption spectroscopy simultaneously at the carbon K- and chlorine L2,3- edges,” Commun. Phys. 7, 304 (2024).
E. Haugen, D. Hait, V. Scutelnic, T. Xue, M. Head-Gordon, S. R. Leone, “Ultrafast X-ray spectroscopy of intersystem crossing in hexafluoroacetylacetone: chromophore photophysics and spectral changes in the face of electron-withdrawing groups” J. Phys. Chem. A 127, 634-644 (2023).
M. Epshtein, B. N. C. Tenorio, M. L. Vidal, V. Scutelnic, Z. Yang, T. Xue, A. I. Krylov, S. Coriani, S. R. Leone, “Signatures of the bromine atom and open-shell spin-coupling in the X-ray spectrum of bromobenzene cation,” J. Am. Chem. Soc. 145, 3554-3560 (2023).
E. Ridente, D. Hait, E. A. Haugen, A. D. Ross, D. M. Neumark, M. Head-Gordon, S. R. Leone, “Femtosecond symmetry breaking and coherent relaxation of methane cations at the carbon K-edge,” Science 380, 713-717 (2023).
