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

The B̃(2)A(')-X̃(2)A(') transition of the prototypical thiophosphoryl radical, H(2)PS, was observed for the first time using laser-induced fluorescence and single vibronic level emission spectroscopy. H(2)PS and its deuterated isotopologues, D(2)PS and HDPS, were produced in a pulsed supersonic discharge jet from a precursor mixture of Cl(3)PS and H(2) or D(2) or an H(2)/D(2) mixture in high-pressure argon. High level ab initio calculations of the lowest three doublet electronic states helped in the definitive assignment of the B̃-X̃ transition, which involves electron promotion from the π to the π∗ orbital. Vibrational frequencies were determined for several modes of each isotopologue in the X̃ and B̃ 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.