Dissociative photoionization of sulfur chlorides and oxochlorides: thermochemistry and bond energies based on accurate appearance energies.

The dissociative photoionization of four compounds, SCl(2), S(2)Cl(2), SOCl(2), and SO(2)Cl(2), were measured with threshold and imaging photoelectron photoion coincidence spectrometry (TPEPICO and iPEPICO). In all systems, the molecular ion loses a chlorine atom in a fast dissociation. The 0 K appearance energies of the first chlorine-loss fragment ions were determined to be 12.252 +/- 0.012 eV, 11.205 +/- 0.003 eV, 11.709 +/- 0.003 eV, and 12.505 +/- 0.003 eV, respectively. SCl(2) was measured on the laboratory-based TPEPICO instrument, in which the second Cl-loss dissociation could not be observed within the available photon energy. For S(2)Cl(2)(+) and SOCl(2)(+), the appearance energy of the fragment ion after two chlorine-loss dissociations were determined to be 13.32 +/- 0.02 eV and 14.88 +/- 0.02 eV, respectively. On the basis of the analysis of the breakdown curves, it was concluded that assuming three-dimensional translational degrees of freedom yields a more reliable statistical model of the product energy distributions. The literature heat of formation of the neutral precursor molecule thionyl chloride, SOCl(2) does not agree with our results based on the SO(+) cation and is revised by more than 10 kJ mol(-1) to -198.2 +/- 2.4 kJ mol(-1). A particularly broad Franck-Condon gap with vanishingly small threshold electron signal in the photon energy range for the second Cl-loss reaction in SO(2)Cl(2)(+) is discussed with regard to the mechanism of threshold ionization.