Nitrogen molecule-dimethyl sulfide complex investigated by fourier transform microwave spectroscopy and ab initio calculation

This paper presents an extension of the preceding talk on the FTMW spectroscopy of \chem{N_2}-ES (ethylene sulfide), namely the results on \chem{N_2}-DMS (dimethyl sulfide). We have previously investigated two \chem{N_2} complexes: \chem{N_2}-DME (dimethyl ether), for which we reported a prelimanary result,\footnote{Y. Kawashima, Y. Tatamitani, Y. Morita, and E. Hirota, ${61st International Symposium on Molecular Spectroscopy}$, TE10 (2006)} and \chem{N_2}-EO (ethylene oxide).\footnote{Y. Kawashima and E. Hirota, ${J. Phys. Chem. A}$ \bf{2013} \it{117} \rm{13855}} We have observed the ground-state rotational spectrum of the \chem{N_2}-DMS complex, i.e. $c$-type transitions in the frequency region from 5 to 24 GHz, which we assigned to the normal, \chem{^{15}N_2}-DMS, and \chem{^{15}NN}-DMS species of the \chem{N_2}-DMS. We have found both the ortho and para states for the \chem{^{14}N_2}-DMS and \chem{^{15}N_2}-DMS species. In the case of the \chem{^{15}N_2}-DMS, some transitions with $K_{a}$ = 2 and 3 were observed slightly split by the internal rotation of the two methyl tops of the DMS. The observed spectra of the \chem{^{15}N_2}-DMS were analyzed by using the XIAM program. In the case of the para state of the \chem{^{15}N_2}-DMS, three rotational and five centrifugal distortion constants with the $V_{3}$ barrier to the methyl group internal rotation, whereas, in the case of the ortho state of the \chem{^{15}N_2}-DMS, two more centrifugal distortion constants, $\Phi_{JK}$ and $\Phi_{KJ}$, were needed to reproduce the observed spectra. For the \chem{N_2}-DMS complex, we concluded that the \chem{N_2} moiety was located in a plane perpendicular to the C-S-C plane and bisecting the CSC angle of the DMS. \\ We have carried out ab initio molecular orbital calculations at the level of MP2 with basis sets 6-311++G(d, p), aug-cc-pVDZ, and aug-cc-pVTZ, to complement the information on the intracomplex motions obtained from the observed rotational spectra. We have applied a natural bond orbital (NBO) analysis to the \chem{N_2}-DMS and \chem{N_2}-ES to calculate the stabilization energy CT (=$\Delta E_{\sigma\sigma}$), which was closely correlated with the binding energy $E_{B}$, as found for other related complexes