Towards the complete analysis of the rotational spectrum of (CH3)3SnCl

The rotational spectrum of the symmetric top trimethyl tin chloride (CH3)3SnCl has been studied using a pulsed molecular beam Fourier transform microwave spectrometer in the frequency range from 3 to 24 GHz. The spectrum is exceedingly complicated by the internal rotation motions of the three equivalent methyl tops, the high number of Sn- and Cl-isotopes and the quadrupole hyperfine structure of the chlorine nucleus. In this paper, we present the microwave spectrum, ab initio calculations, permutation inversion (PI) group-theoretical considerations, Stark-effect measurements and finally the K = 0 assignments and fits of the different torsion-rotation species. Based on the Stark-effect measurements, the dipole moment is μ = 3.4980(30) D. Due to ΔK=±1-mixing effects we observe linear Stark-effect behavior and additional quadrupole splitting for some K=0 torsion-rotation transitions in (CH3)3SnCl, which can be group-theoretically explained. The symmetric rotor fit of A1 and A2 torsion-rotation states leads to an effective B-constant of 1680.040124(92) MHz for the main isotopologue (CH3)3120Sn35Cl. A global fit of 182 K=0 torsion-rotation transitions yields a V3 torsional barrier of 1.774(6) kJ.