Photoelectron Spectroscopy and Ionic Fragmentation of OSeCl₂ and Its Analogue OSCl₂ under VUV Irradiation

The electronic structure and the dissociative ionization of selenium oxychloride, OSeCl₂, have been investigated in the valence region by using results from both photoelectron spectroscopy (PES) and synchrotron-based photoelectron photoion coincidence (PEPICO) spectra. The PES is assigned with the help of quantum chemical calculations at the outer-valence Green’s function (OVGF) and symmetry adapted cluster/configuration interaction (SAC-CI) levels. The first energy ionization is observed at 11.47 eV assigned to the ionization of electrons formally delocalized over the Se, Cl, and O lone pair orbitals. Irradiation of OSeCl₂ with photons in the valence region leads to the formation of OSeCl₂^•+, OSeCl⁺, SeCl₂^•+, SeCl⁺, and SeO^•+ ions. Furthermore, the inner shell Se 3p, Cl 2p, and Se 3s electronic regions of OSeCl₂ together with S 2p, Cl 2p, and S 2s electronic regions of thionyl chloride, OSCl₂, have been studied by using tunable synchrotron radiation. Thus, total ion yield spectra and the fragmentation patterns deduced from PEPICO spectra at the various excitation energies have been studied. Cl⁺, O^•+, and Se^•+ ions appear as the most intense fragments in the OSeCl₂ PEPICO spectra, like in the sulfur analogue OSCl₂, whose photofragmentation is dominated by the Cl⁺, O^•+, and S^•+ ions. Fragmentation processes in OSCl₂ leading to the formation of the double coincidences involving atomic ions appear as the most intense in the PEPIPICO spectra.