Electron and ion spectroscopy of azobenzene in the valence and core shells.

This article focuses on a comprehensive experimental and theoretical investigation of azobenzene (AB), a prototype molecular photoswitch, examining its valence and core photo-ionization, excitation, and fragmentation processes using synchrotron radiation techniques and advanced quantum chemical methods. The study combines photoelectron spectroscopy (PES), x-ray photoelectron spectroscopy (XPS), near edge x-ray absorption fine structure (NEXAFS), and photoelectron-photoion coincidence (PEPICO) measurements with multiconfigurational restricted active space self-consistent field (RASSCF) and second-order perturbation theory (RASPT2) calculations to characterize the electronic structure and fragmentation pathways of the trans-isomer of AB. Key findings include the assignment of valence ionization bands dominated by π and lone pair orbitals, identification of primary fragmentation channels involving phenyl ring loss and N2 elimination, and detailed interpretation of carbon and nitrogen K-edge core-level spectra. The study demonstrates that carbon and nitrogen K edges provide sensitive, site-specific probes suitable for tracking photoinduced electronic dynamics in AB, supporting future time-resolved core-level spectroscopic investigations of molecular photoswitches.