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 a1 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.

Vapor Phase Electronic Absorption and MCD Spectra for Dimethyl Sulfide, Dimethyl Selenide, and Dimethyl Telluride in the UV Region

“…The absorption spectra compare favorably with those reported earlier 4,7. For example, bands I, II, and III (all in µm -1…”

“…7 The MCD in this region is quite strong and mirrors the complexity of the absorption, but unfortunately little can be concluded from the present spectra. The complete band was not accessible in the present study due to the measurement limit, and the intermediate energy position of the states associated with this band between the several to lower energy and many more to higher energy 7 precludes any satisfactory B term interpretation.…”

“…It may be remarked that the 1b 1 f 4a 1 , 3B 1 assignment was one of those suggested earlier. 7 The MCD thus provides experimental support for this n X f σ* assignment of band II and also serves to strengthen the n X f (n + 1)p 4A 1 Rydberg assignment for band III.…”

“…It has been suggested that band II red shifts relative to band III for Me 2 Se and Me 2 Te, so that it overlaps or is combined with band I. 7 This suggestion is certainly reasonable in view of the n X f σ* character of the valence transition. The σ* 4a 1 orbital is expected to be relatively more stable for Se and Te (less antibonding) than for S due to weaker covalent bonding.…”

Laser photoelectron spectroscopy: spectroscopy and dynamics of excited states in small and medium‐sized molecules

“…PES shows this feature to be an origin (a = 5), while the quantum defect is near integer. The lowest member of this series (n = 4) has been observed in one-photon absorption spectroscopy at N 228 nm [289,299,3001, Higher energy members of this series, labeled 11, are observed in Figure 52 and have been seen in previous one-photon absorption studies . The assignment is taken as n's' + 3hl.…”