Ultraviolet Absorption Spectrum of Cyclic S2O in Solid Ar

Disulfur monoxide dispersed in solid Ar at 15 K was irradiated with light at 308 nm from an XeCl excimer laser to form cyclic S 2 O, denoted cyc -S 2 O; cyc -S 2 O was identified according to infrared absorption lines reported previously. Using a similar technique to produce cyc -S 2 O, we recorded both infrared and ultraviolet absorption spectra of the same matrix sample before and after photolysis at various stages. A progression recorded in a range 330−370 nm with intervals ∼580 cm -1 correlates well with variations in intensities of infrared absorption lines of cyc -S 2 O. On the basis of characteristics of this observed progression and calculations of vertical excitation energy and oscillator strength using the time-dependent density-functional theory, we tentatively assign this progression to an electronic transition 2 1 B 1 ← X 1 A 1 of cyc -S 2 O; the observed progression is associated with the S−S stretching (ν 2 ) mode in the excited state. The 2 1 B 1 state lies ∼77.7 kcal mol -1 (27 166 cm -1 ) above the ground electronic state.