Fourier Transform Microwave Spectra of the Nitrogen Molecule-Ethylene Sulfide and Nitrogen Molecule-Dimethyl Sulfide Complexes.

We recorded the rotational spectra of N-ethylene sulfide (ES) and N-dimethyl sulfide (DMS) including the N and NN isotopomers in the frequency range of 5-25 GHz by using a Fourier transform microwave spectrometer. The b-type transitions for the ortho and para states of N-ES and N-ES and c-type transitions of N-DMS and N-DMS were observed. The NN-ES and NN-DMS species were found to exist in two isomeric forms: inner (NN-ES and NN-DMS) and outer (NN-ES and NN-DMS). Neither the -ES nor -DMS complexes showed weak accompanying spectra, which had been observed for N-ethylene oxide (EO). This is because the potential barriers to internal rotation of ES and DMS are higher than that of EO. The spectra were analyzed by an A-reduced asymmetric-top rotational program with less than 4 kHz standard deviation, except for the NN-DMS and NN-DMS complexes. Rotational, centrifugal distortion, and nuclear electric quadrupole coupling constants were determined by the spectral analysis. The V potential barrier to internal rotation of the two equivalent methyl groups of DMS in the ortho and para states of the N-DMS complex was determined to be about 740 cm. We performed ab initio calculations in order to complement the information on the intracomplex motions obtained from the experimental spectra.