Microwave Spectrum of γ-Thiobutyrolactone

Abstract

The microwave spectrum of γ-thiobutyrolactone has been observed and measured in the vibra-tional ground state and in several excited states of the ring-bending and ring-twisting modes. From the value of the μ_c component of the dipole moment and inertial-defect considerations the ring skeleton was shown to be non-planar. The average intensity ratio for the rotational transitions between the ground and excited vibrational states indicates that the first excited state of the ring-bending and ring-twisting modes are ~ 120 cm^-1 and ~ 250 cm^-1 above the ground state respectively. These two out-of-plane ring vibrations are essentially independent and the ring-bending vibration is governed by a nearly harmonic potential energy function. The components of the dipole moment were determined by the Stark effect to be μ_a = 3.770 ± 0.001 D, μ_b = 1.818 ± 0.044 D and μ_c = 0.832 ± 0.018 D, leading to μ_total = 4.268 ± 0.023 D. The rigidity of the γ-thiobutyrolactone ring is discussed in relation to those of related molecules.