Heavy atom nitroxyl radicals. V. An experimental and ab initio study of the previously unknown H2PS free radical

The B2A - X2A transition of the prototypical thiophosphoryl radical, H2PS, was observed for the first time using laser-induced fluorescence and single vibronic level emission spectroscopy. H2PS and its deuterated isotopologues, D2PS and HDPS, were produced in a pulsed supersonic discharge jet from a precursor mixture of Cl3PS and H2 or D2 or an H2/D2 mixture in high-pressure argon. High level ab initio calculations of the lowest three doublet electronic states helped in the definitive assignment of the B − X transition, which involves electron promotion from the π to the π* orbital. Vibrational frequencies were determined for several modes of each isotopologue in the X and B states and found to be in accord with theoretical predictions. Although a line-by-line rotational analysis was not possible, the observed band contours are consistent with the geometries obtained from our ab initio calculations. Theory indicates that PS bond length increases upon electronic excitation, while the pyramidalization of the radical does not change significantly.