PULSE Pizza Photon Science Seminar Series B57 Hallway by the Breakroom from 1:30pm-2:30pm
SLAC, Redtail Hawk Conference Room 108A
Join from PC, Mac, Linux, iOS or Android:https://stanford.zoom.us/j/99715088163?pwd=S0kRApnf05paGm2RugqUj73FBc0gFp.1
Meeting ID: 997 1508 8163
Password: 274495
Speaker: Dr. Markus Guehr, Deutsches Elektronen Synchrotron DESY and Physical Chemistry, Chemistry Department University of Hamburg
Program Description
Many molecular light-energy conversion processes in nature occur on an ultrafast (sub-picosecond) timescale. The conversion process often occurs at conical intersections, which are regions in molecular phase space characterized by degenerate potential energy surfaces and a linear lifting of energy degeneracy. To fully monitor and understand the ultrafast dynamics of a molecule, a combined knowledge of two realms—nuclear geometry and electronic structure—is required. Specifically, this involves understanding the molecular geometry changes that drive the molecule towards regions of strong coupling among electronic states, as well as the resulting changes in these states.
In this talk, the electronic and nuclear geometry perspectives will be combined in time-resolved studies on the thionated nucleobase 2-thiouracil (2-tUra). We use time-resolved soft x-ray photoemission spectroscopy performed at the FLASH FEL to gain insight into changes in the molecular electronic structure during internal conversion1. To investigate the light-induced changes in molecular geometry, we employ Coulomb-Explosion Imaging at the European XFEL. We use hydrogen atoms as messengers and discover the de-planarization of the molecular geometry on its path towards the conical intersection. The combination of both methods provides unprecedented experimental insight into the light-energy conversion dynamics in molecules2.
(1) Mayer, D.; Lever, F.; Picconi, D.; Metje, J.; Alisauskas, S.; Calegari, F.; Düsterer, S.; Ehlert, C.; Feifel, R.; Niebuhr, M.; Manschwetus, B.; Kuhlmann, M.; Mazza, T.; Robinson, M. S.; Squibb, R. J.; Trabattoni, A.; Wallner, M.; Saalfrank, P.; Wolf, T. J. A.; Gühr, M. Following Excited-State Chemical Shifts in Molecular Ultrafast x-Ray Photoelectron Spectroscopy. Nat Commun 2022, 13 (1), 198. https://doi.org/10.1038/s41467-021-27908-y.
(2) Jahnke, T.; Mai, S.; Bhattacharyya, S.; Chen, K.; Boll, R.; Castellani, M. E.; Dold, S.; Frühling, U.; Green, A. E.; Ilchen, M.; Ingle, R.; Kastirke, G.; Lam, H. V. S.; Lever, F.; Mayer, D.; Mazza, T.; Mullins, T.; Ovcharenko, Y.; Senfftleben, B.; Trinter, F.; Atia-Tul-Noor; Usenko, S.; Venkatachalam, A. S.; Rudenko, A.; Rolles, D.; Meyer, M.; Ibrahim, H.; Gühr, M. Direct Observation of Ultrafast Symmetry Reduction during Internal Conversion of 2-Thiouracil Using Coulomb Explosion Imaging. Nat Commun 2025, 16 (1), 2074. https://doi.org/10.1038/s41467-025-57083-3.
