Some Effects of Vibration and Molecular Structure on Internal Rotation in CH2DSH and CHD2SH

The $\text{J\hspace{0.17em}=\hspace{0.17em}1\hspace{0.17em}←\hspace{0.17em}0, ΔK\hspace{0.17em}=\hspace{0.17em}0}$ lines have been assigned in the microwave rotational spectra for the partially deuterated methyl mercaptans. The fine structure of the transitions for the torsional ground state has been analyzed on the basis of internal rotation and molecular structure. It is necessary to introduce a $V_1$ $\cos \alpha$ term into the effective potential energy for internal rotation to account for the relative splittings. Although it is not possible to determine a unique value for $V_1$ , the limits $\text{1.5}{\mathrm{cm}}^{\text{−1}}{\mathrm{\hspace{0.17em}\le \hspace{0.17em}|\hspace{0.17em}V}}_1\text{\hspace{0.17em}|\hspace{0.17em}≤\hspace{0.17em}10}{\mathrm{cm}}^{\text{−1}}$ are obtained. From the splittings it is possible to determine an improved value of 3°5′ for the so‐called C–S tilt with respect to the methyl axis. The staggered configuration for the thiol–methyl orientation is found to be the minimum in the threefold potential energy.