The first high-resolution analysis of the 10-μm absorption of thioformaldehyde

Abstract

The 10 μm region of thioformaldehyde (H 2CS) has been recorded at high resolution (0.005 cm −1) using a Fourier transform spectrometer. H 2CS was produced by low-pressure pyrolysis of a gas flow of C 3H 5SCH 3 in Ar at 560 °C or CH 3SCl at 1150 °C, which was introduced into a multipass White cell with an optical path length of 32 m. Forty scans were recorded for the range 750–1400 cm −1 at a total pressure of 0.15 mbar. A thorough analysis of the three lowest wavenumber fundamental bands, ν 3, ν 4 and ν 6, which fall in this region, has been carried out using a Hamiltonian model, which takes explicitly into account the numerous resonances affecting the ro-vibrational energy levels; especially the massive A-type Coriolis resonance between the out-of-plane wagging mode, ν 4, and the in-plane rocking mode, ν 6. These two modes are only separated by 0.83 cm −1, and they are thoroughly mixed. From the fittings, the following band centers were derived: ν o ( ν 4)=990.18213(40) cm −1, ν o ( ν 6)=991.02021(50) cm −1 and ν o ( ν 3)=1059.20476 (30) cm −1 where the uncertainties are one standard deviation. In addition, a number of relative line intensities were measured permitting the determination of relative values of the first-order transition moments and therefore relative band intensities for all three bands. Finally, a comprehensive list of line wavenumbers and relative intensities has been generated.