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

Abstract

Electronic absorption and magnetic circular dichroism spectra for (CH3)2X, X = S, Se, and Te, in the vapor phase were measured in the range 2.5−5.3 μm-1 with a spectral bandwidth of ≤0.003 μm-1. The spectra show well-resolved vibrational structure for the nX → (n + 1)p Rydberg system with positive MCD B terms for (CH3)2Se and (CH3)2Te, but a negative B term for (CH3)2S. The difference in the MCD spectra is interpreted in terms of the influence of magnetic coupling with the broad nX → σ* valence transition, which lies rather close in energy to the Rydberg system for X = S, but is separated to lower energy for X = Se or Te. The interpretation requires a nX → σ* transition assignment of 1A1 → 1B1 and provides support for the most recent 1A1 symmetry assignment of the nX → (n + 1)p Rydberg excited state. The assignment of several weak, previously unreported, bands for X = Se and Te is also given.