Exploring the capabilities of optical pump X-ray probe NEXAFS spectroscopy to track photo-induced dynamics mediated by conical intersections

• DOI: 10.1039/c9fd00073a
• Publication Date: 2019-09-25T07:43:38Z
• Authors: Francesco Segatta; Artur Nenov; Silvia Orlandi; Alberto Arcioni; Shaul Mukamel; Marco Garavelli
• Keywords: XANES; Azobenzene

X-ray spectroscopy is gaining a growing interest in the scientific community, as it represents versatile and powerful experimental toolbox for probing dynamics of both core valence electronic excitations, nuclear motions material structure, with element site specificity. Among various based techniques, near-edge absorption fine structure (NEXAFS) spectroscopy, which investigates energy probability resonant core-to-valence transitions, has started to be applied organic molecules: recent UV-pump probe time-resolved NEXAFS experiment [Wolf et al., Nat. Commun., 2017, 8, 1] shown capability technique provide information about ultrafast internal conversion between bright ππ* dark nπ* states nucleobase thymine. In present contribution we introduce an accurate theoretical approach simulation spectra molecules, employing azobenzene test case. The calculations, levels transition probabilities were here performed high level multiconfigurational method, restricted active space self consistent field (RASSCF/RASPT2). GS- nπ*-NEXAFS obtained on top key molecular geometries (as optimized cis, trans conical intersection(s) structures) well along fundamental isomerization coordinates (namely, symmetric asymmetric bendings phenyl rings, torsion around central dihedral). We eventually characterize explain origin simulated signals, highlighting specific signatures that make possible follow excited state evolution from Franck-Condon point, towards intersection(s).