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 S₂O, denoted cyc-S₂O; cyc-S₂O was identified according to infrared absorption lines reported previously. Using a similar technique to produce cyc-S₂O, 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-S₂O. 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 ¹B₁ ← X¹A₁ of cyc-S ₂O; the observed progression is associated with the S-S stretching (ν₂) mode in the excited state. The 2 ¹B₁ state lies ∼77.7 kcal mol^-1 (27 166 cm^-1) above the ground electronic state.