The millimetre-wave spectrum of trimethylene sulphide Vibration-rotation coupling between thev=2 andv=3 ring-puckering excited states

Abstract

The microwave spectra of trimethylene sulphide in the ground and the first eight excited states of the ring-puckering vibration have been measured in the frequency region 26·5‥–250 GHz. Very large Coriolis coupling interaction effects have been observed for the high-J spectra of the v=2 and 3 ring-puckering states in addition to those previously observed between the states v=0 and v=1. A two-state vibration-rotation interaction analysis of these effects has allowed the determination of a vibrational energy spacing ΔE 23=11·97304(1) cm−1. The ring-puckering potential energy function for this molecule has been determined from a simultaneous weighted least-squares fit of the rotational constants and vibrational energy intervals. The observed ring-puckering dependence of the quartic centrifugal distortion constants, including a small dependence of Δ J and δ J , is well accounted for in terms of the ring-puckering potential function obtained in this work.