Determination of the Molecular Constants for Interacting Bright and Dark States: Analysis of the High-Resolution Infrared Spectrum of the ν8 Band of Sulfine, H2CSO

Abstract Gas-phase infrared spectra of the transient molecule sulfine, H 2 CSO, have been recorded in pyrolysis experiments using methanesulfinyl chloride or dimethyl sulfoxide as starting materials. Two strong vibrational fundamentals, ν 4 ( a ′, 1175 cm −1 ) and ν 8 ( a ″ 762 cm −1 ), have been observed at low resolution in the 1400-700 cm −1 region. The ν 8 band has been recorded at high resolution and a detailed analysis of the rotational structure has been carried out. Numerous excited state perturbations result from |Δ K a | = 2 A -type and |Δ K a | = 1 B -type Coriolis interactions with the 7 2 vibrational state at 784.2 cm −1 . Although 2ν 7 band transitions could not be directly observed, a complete analysis of the perturbed rotational structure has been possible, using a Hamiltonian which includes both types of Coriolis interactions. Accurate molecular constants have been obtained for both states with only two interaction constants, one for each mechanism. A few weak perturbations at very high K a values could not be fitted with this scheme and are assigned to high order Coriolis interactions with the 6 1 level at 866 cm −1 .