Rotational spectrum of the Ar-dimethyl sulfide complex

The rotational spectra of three isotopomers of the Ar-dimethyl sulfide (DMS) complex - normal, 34S, and 13C species - were measured in the frequency region from 3.7 up to 24.1 GHz by Fourier transform microwave spectroscopy. The normal species yielded 43 a-type and 79 c-type transitions. No Ar tunneling splitting was observed, while many transitions were split by the internal rotation of the two methyl tops of the DMS unit. In cases where the K-type splitting was close to that due to methyl internal-rotation, several forbidden transitions were observed that followed b-type selection rules. All of the observed transition frequencies were analyzed simultaneously using a phenomenological Hamiltonian also used in previously published work describing the Ar-dimethyl ether (DME) and Ne-DME complexes. The rotational and centrifugal distortion constants and the potential barrier height to methyl-top internal rotation, V3, were determined. The rotational constants were consistent with an Ar-DMS center of mass (cm) distance of 3.796 (3) Å and a S-cm-Ar angle of 104.8 (2)°. The V3 potential barrier obtained, 736.17 (32) cm−1, was 97.8% of the DMS monomer barrier. By assuming a Lennard-Jones-type potential, the dissociation energy was estimated to be 2.4 kJ mol−1, which was close to the value for Ar-DME, 2.5 kJ mol−1.