Fragmentation of the valence electronic states of PSCl3+ studied by threshold photoelectron–photoion coincidence spectroscopy

Abstract

The threshold photoelectron spectrum and threshold photoelectron–photoion coincidence spectrum of PSCl3 are reported in the range 9.5–22.5 eV. Tunable ionising radiation with a resolution of 0.3 nm is provided from a synchrotron source coupled to a vacuum–UV monochromator. The coincidence spectra are recorded continuously as a function of photon energy, allowing yields of the fragment ions to be obtained. The ground state of PSCl3+ is bound with respect to dissociation, whereas the five lowest excited electronic states dissociate by P–Cl bond cleavage to PSCl2+. An upper limit of 629 ± 30 kJ mol−1 is determined for the enthalpy of formation of PSCl2+ at 298 K. For energies above ca. 15 eV, fragment ions corresponding to multiple bond cleavages are observed; PSCl+ and PCl2+, PS+ and PCl+. Because of uncertainties in thermochemistry, it is possible only for PS+ to determine the neutrals that form with this fragment cation. Translational kinetic energy releases have been measured into PSCl2+ + Cl at the energies of the Franck–Condon maxima of the valence states of PSCl3+, and the results compared with models assuming statistical and impulsive dissociation. The kinetic energy data suggest that the six lowest excited states of PSCl3+ decay by a mechanism intermediate between statistical dissociation from the ground state of PSCl3+ following rapid internal conversion and impulsive dissociation from the initially-excited electronic state.