Spectroscopic detection of gas-phase HOSO2

Abstract

The HOSO₂ radical was detected by microwave spectroscopy in a discharge plasma of a SO₂/H₂O gas mixture. The observed spectrum shows tunneling splittings due to the OH torsional motion. A least-squares analysis considering interactions between the two torsional sublevels of the ground vibronic state, 0⁺ and 0⁻, reproduces the observed transition frequencies with a standard deviation of ca. 3 kHz. The splitting between the two torsional sublevels is accurately determined to be 24.3 MHz for HOSO₂ and 0.08 MHz for DOSO₂. The potential barrier for the OH torsional motion is estimated to be 1150 cm⁻¹ from a one-dimensional hindered rotor model.