: 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.