The conformational structures and dipole moments of ethyl sulfide in the gas phase

Abstract

The pure rotational spectrum of ethyl sulfide has been measured from 12 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 13C and 34S isotopomer spectra of these conformers effectively account for all of 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 (Hartree–Fock)/6-31* and MP2 (second-order Møller–Plesset)/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.

High Resolution Electronic Spectroscopy of o- and m-Toluidine in the Gas Phase. Barrier Height Determinations for the Methyl Group Torsional Motions

“…The resulting spectra were fit using the jb95 leastsquares fitting program. 11 Theoretical calculations were performed using the Gaussian 03 suite of programs 12 to supplement the experiments. Geometry optimizations of both o-toluidine and m-toluidine in the ground state were performed at the MP2 level of theory with a 6-31G** basis set.…”

Fourier Transform Microwave Spectrum and ab Initio Study of Dimethyl Methylphosphonate

“…Because of the expected uncertainties associated with the molecular Hamiltonian, it was desirable to record a broad region of the spectral region available. Initially this was accomplished by recording 1-GHz segments of the spectrum and then adding these together using the spectral fitting program developed by Plusquellic (9). With the automated scanning features of the software that controls the FTMW instrument (5), it takes 1.5 h to record 1 GHz of spectrum using 10 nozzle pulses/step (at a 10-Hz repetition rate) and 500 kHz/step.…”

Spectroscopy and ionization thresholds of π-isoelectronic 1-phenylallyl and benzylallenyl resonance stabilized radicals

“…Rotational band contours were simulated according to previous methods using JB95 4,19 and compared to experimental spectra.…”