High resolution rovibrational analysis of dimethyl sulfide spectrum in the 10 µm atmospheric window combining supersonic jet-quantum cascade laser and FTIR spectroscopies

Abstract

The rovibrational spectrum of the v14 CH3-bending mode of dimethyl sulfide CH3SCH3 was recorded in the 945–1005 cm−1 spectral region combining data from a tunable infrared quantum cascade laser spectrometer coupled to a pulsed slit jet and from a high resolution Fourier transform spectrometer coupled to a room temperature gas absorption cell. The characteristic PQR band contour of a vibrational mode with a b1 symmetry species in the C2v group was observed with both infrared methods but the rovibrational cooling achieved in the pulsed supersonic expansion (20 K in rotation) proved to be essential for starting the rovibrational analysis of such asymmetric top molecule. Internal rotation splittings were recently observed and analyzed in the ground and first torsional excited states. However, they are expected to be very small and could not be resolved in the v14 state using our infrared spectroscopic probes. Therefore a classic reduced effective Hamiltonian of an asymmetric rigid rotor was used. Finally, 1119 transitions from both jet-cooled and room temperature experiments were assigned and included in a global fit with J ≤ 29. A total of 9 rovibrational parameters including pure rotational constants as well as quartic centrifugal distortion constants were determined with high accuracy. These parameters can be used to produce a reliable line-list for an atmospheric detection of DMS.