Vacuum ultraviolet absorption spectra of dimethylsulfide, dimethylselenide, and dimethyltelluride

Abstract

The vapor phase absorption spectra of dimethylsulfide, dimethylselenide, and dimethyltelluride are reported for the 40 000–80 000 cm−1 vacuum ultraviolet spectral region. Three Rydberg series for each compound were assigned which converge on the ionization potentials of 8.706 ± 0.010, 8.400 ± 0.010, and 7.926 ± 0.010 eV for dimethylsulfide, dimethylselenide, and dimethyltelluride, respectively. These ionization potentials and corresponding Rydberg series members are assigned as originating from the central atom valence p orbital, which is perpendicular to the plane of the molecule. A correlation of the ionization potentials calculated for these molecules to ionization potentials of corresponding rare gases is presented. The term values of Rydberg members of the dimethyl chalcogens are also correlated to the term values of allowed atomic Rydberg series in the rare gases, thus atomic nomenclature is used in the assignment of the molecular Rydberg series. Higher energy absorptions in the spectra of dimethylselenide and dimethyltelluride are assigned as originating from a nonbonding orbital of a 1 symmetry localized on the central atom. In the three spectra, vibrational progressions are analyzed with respect to ground state totally symmetric vibrational frequencies. Utilizing Franck‐Condon factors and harmonic oscillator potentials, the excited state geometry changes were found to be similar, where the C–X–C (X=S, Se, or Te) bond angles are essentially unchanged and the C–X bond distances are changed approximately 0.040 Å from the ground state bond lengths for all three compounds.