Rotational spectra, internal rotation analysis, dipole moment and structure of methylthiirane

Abstract

The rotational spectrum of methylthiirane, C₃H₆S, has been investigated in the 8–110 GHz frequency range using waveguide and pulsed molecular beam Fourier transform, Stark and source modulation spectrometers. The spectra for the ground vibrational state and the first excited state of methyl torsion and two low-lying vibrations have been measured. A–E splittings due to internal rotation of the methyl group have been observed in these states. The barrier V₃ hindering the internal rotation of the methyl group has been determined to be 13.49(11) kJ mol⁻¹. The rotational spectra of ³⁴S and the three ¹³C isotopomers have been observed in natural abundance and r₀ and r_s structures have been derived for the heavy atom frame of the molecule. Furthermore, the electric dipole moment has been determined from Stark effect measurements as µ_a = 1.6139(25) D, µ_b = 1.1620(36) D and µ_c = 0.2714(23) D.