VIBRONIC ABSORPTION-SPECTRA OF S-3 AND S-4 IN SOLID ARGON

Molecular S4 species show two distinct electronic absorptions, a broad green band centered at 518 nm and a structured red band between 560 and 660 nm in solid argon. The red-absorbing species is converted to the green-absorbing species on irradiation with red light while the green-absorbing species is converted to the red-absorbing species on green light photolysis. These bands are assigned to two different structural isomers of S4 which undergo photoisomerism. The red band shows two vibronic progressions with vibrational intervals of 320 and 590 cm-1. The electronic spectra are correlated with infrared spectra and ab initio calculations for different structural isomers Of S4. Molecular S3 shows relatively sharper bands between 350 and 440 nm, which are assigned to three argon matrix trapping sites based on annealing, vibrational spacings, and isotopic shifts. The origin of the most stable site is only 250 cm-1 above the gas phase band origin. Vibronic analysis provides nu-1' and nu-2' values of approximately 450 and 340 cm-1, respectively, for S3.