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

The threshold photoelectron spectrum and threshold photoelectron photoion coincidence spectrum of PSCl\(_3\) 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 PSCl\(_3^+\) is bound with respect to dissociation, whereas the five lowest excited electronic states dissociate by P-Cl bond cleavage to PSCl\(_2^+\). An upper limit of 629 ± 30 kJ mol\(^{-1}\) is determined for the enthalpy of formation of PSCl\(_2^+\) at 298K. For energies above ca. 15 eV, fragment ions corresponding to multiple bond cleavages are observed; PSCl\(^+\) and PCl\(_2^+\), 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 PSCl\(_2^+\) + Cl at the energies of the Franck-Condon maxima of the valence states of PSCl\(_3^+\), and the results compared with models assuming statistical and impulsive dissociation. The kinetic energy data suggest that the six lowest excited states of PSCl\(_3^+\) decay by a mechanism intermediate between statistical dissociation from the ground state of PSCl\(_3^+\) following rapid internal conversion and impulsive dissociation from the initially-excited electronic state.