Ultrapure gaseous COS exhibits a broad absorption continuum in the near-ultraviolet region which starts at 2550 A and extends to below 2000 A with a rounded maximum at 2225 A. Semiempirical molecular orbital calculations, with the inclusion of the sulfur d orbitals, indicate this continuum to correspond to a π→ π* transition since the lowest lying n → π* type state appears at considerably higher energies. Photolysis in this region affords CO (ψ = 1.81 at 2537 and 2288 A) and sulfur. The primary step yields S atoms at least 74% of which are formed in the excited (1D) state. The mercury photosensitization at 2537 A affords only triplet-ground-state sulfur atoms. Both singlet- and triplet-state atoms abstractively attack COS to form S2 with the rate ratio, S(1D)/S(3P), being ca. 30. The condensed-phase photolysis is similar to that of the gas phase although the relative yields of triplet- and singlet-state atoms may be altered.
ASJC Scopus subject areas
- Colloid and Surface Chemistry