Optoacoustic spectroscopy with a tunable cw dye laser: forbidden transitions in some unstable sulphur compounds

Abstract

An investigation has been made of the sensitivity of the optoacoustic technique in conjugation with a cw dye laser for the detection of forbidden molecular transitions. Calibration with the a 3 A 2- X 1 A 1 transition of thiophosgene, Cl 2CS, shows that th technique could be used to study band systems with oscillator strengths of f = 10 −10. The method has been applied to the detection of two recently observed forbidden transitions of thioformaldehyde, H 2CS, and a previously unreported transition of disulphur monoxide, S 2O. A vibrational analysis is presented for the S 2O transition, which has upper state frequencies of v′ 1 ≈ 1076 cm −1, v′ 2 ≈ 449 cm −1 302 cm −1. The origin of the system has not been located, but cannot be at higher frequency than 14200 cm −1. The transition has an oscillator strength of ≈ 10 −6, and is assigned to a triplet-singlet transition by its close analogy to the transition of NSF in the same spectral region.