Intermolecular Interactions Between Formaldehyde And Dimethyl Ether And Between Formaldehyde Abd Dimethyl Sulfide In The Complex, Investigated By Fourier Transform Microwave Spectroscopy And Ab Initio Calculations

Abstract

The ground-state rotational spectra of the formaldehyde-dimethyl ether (\chem{H_2CO-DME}) and the formaldehyde-dimethyl sulfide (\chem{H_2CO-DMS}) complexes have been studied by Fourier transform microwave spectroscopy, and $a$-type and $c$-type transitions have been observed and assigned for the \chem{H_2CO} as well as \chem{D_2CO} species of both the complexes. In the case of the \chem{H_2CO-DME}, doublets were observed with the splitting of a few 100 kHz, whereas no such splitting was found for the \chem{H_2CO-DMS}. The observed rotational constants were analyzed to conclude a $C_{\rm{s}}$ geometry, where DME and DMS were bound to \chem{H_2CO} by the two C-H(DME/DMS)---O(\chem{H_2CO}) and the two O(DME)/S(DMS)---H-C(\chem{H_2CO}) hydrogen bonds. The distances $R_{\rm{cm}}$ between the centers of mass of the constituents were determined to be 3.102 and 3.200 \AA for the two complexes, respectively. Both the \chem{H_2CO-DME} and \chem{H_2CO-DMS} complexes were shown by the natural bond orbital (NBO) analysis, to have strong charge transfer interactions between the constituents, as expected from the strong electron-accepting character of the \chem{H_2CO}.