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

Abstract

The rotational spectrum of methylthiirane, C ₃ H ₆ S, 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 V ₃ hindering the internal rotation of the methyl group has been determined to be 13.49(11) kJ mol ⁻¹ . The rotational spectra of ³⁴ S and the three ¹³ C isotopomers have been observed in natural abundance and r ₀ 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.