Heavy atom nitroxyl radicals. III. Identification of the Cl(2)P=S free radical in the gas phase by laser spectroscopy and ab initio calculations.

The dichlorothiophosphoryl (Cl(2)PS) free radical has been identified in the gas phase for the first time by a combination of laser-induced fluorescence and single vibronic level emission spectroscopy. High level ab initio calculations of the properties of the ground and first two excited states have been undertaken to aid in the interpretation of the data. The radicals were produced by an electric discharge through a dilute mixture of Cl(3)PS in high pressure argon at the exit of a pulsed supersonic expansion. An extensive band system was observed in the 760-560 nm region and has been assigned as the B (2)A(')-X (2)A(') electronic transition in which an electron in the ground state pi orbital is promoted to the pi( *) orbital. Three excited state and four ground state vibrational frequencies and their chlorine isotope effects have been measured and found to be in good accord with the theoretical predictions. Theory indicates that the radical is nonplanar in the ground state with increased pyramidalization and a longer PS bond in the first (A (2)A(") n-pi( *)) and second excited electronic states.