The pure rotational spectrum of ethyl sulfide has been measured from 12 gHz to 21 GHz in a 1 K Jet-cooled expansion using a Fourier-transform microwave (FTMW) spectrometer. Prominent features in the spectrum are assigned to transitions from three conformational isomers. Additional assignments of the 13S isotopomer spectra of these conformaers effectively account for all fo the remaining transitions in the spectrum. Accurate heavy-atom substitution structures are obtained via a Kraitchman analysis of 14 rotational parameter sets, permitting definitive identification of the molecular structures of the three conformers. Two of the structures designated as the gauche-gauche (GG) and trans-trans (TT) conformers have symmetric forms with C2 and C2v symmetries, respectively, and the third trans-gauche (TG) configuration is asymmetric. The components of the electric dipole moment along the principal inertial axes have been determined from Stark measurements and are consistent with these structural assignments. Detailed comparisons are made with the calculated geometries, dipole moments and energy-level ordering at both the HF/6-31* and MP2/6-311** levels of theory. Significant discrepancies are found, which are mainly attributed to errors in the calculated dihedral angles that define the different conformations. A graphical-user-interface computer program has aided in the identification and assignment of entangled hybrid-band spectra from the different conformers and isotopomers in this study. The program includes features that enable real-time refinement of rotational constants and hybrid band intensities through visual comparisons of the experimental data with simulated spectra. Capacities also exist to rapidly assign quantum number labels for least-squares fitting purposes.
Citation: Journal of Chemical Physics
Issue: No. 7
Pub Type: Journals
conformational isomers, fourier transform microwave spectra, permanent dipole moments, rotational spectrum