The torsion-torsion-bending spectrum of S-methyl thioformate

Abstract

The far infrared spectral region of S-methyl thioformate is explored using a theoretical model of reduced dimensionality depending on three large amplitude vibrations: the torsions of the methyl and the COH groups and the CSC bending mode. A Hamiltonian of reduced dimensionality is solved variationally to determine the low-lying energy levels. To evaluate the effect of the S←O substitution, the spectroscopic properties are compared with those of the O-analog, methyl-formate, an abundant astrophysical molecule. The barrier of methyl internal rotation of S-methyl thioformate is predicted to be three times lower than the one of methyl formate. The A/E splitting of the ground vibrational state has been estimated to be 0.475 cm−1. The A/E components of the fundamental frequencies are predicted at 79.523/68.459 cm−1 (methyl torsion), 251.564/251.717 cm−1 (COH torsion), and 255.056/252.523 cm−1 (CSC bending). Small Fermi interactions between the methyl torsion overtone and the CSC bending mode are observed.