INFRARED AND VISIBLE SPECTRA OF SMALL SELENIUM CLUSTERS (N = 2, 3, 4) IN SOLID ARGON

Se2, generated by thermal decomposition of selenium vapor, was condensed with argon at 12 K; in concentrated samples, both Se2 and Se4 Were isolated in good yield. The forbidden transition between the fine structure components of the X 3SIGMA(g)-state of Se2 was observed directly: DELTAnu10 = 513.9 +/- 0.1 cm-1. Two different Se4 isomers were observed: One isomer is characterized by an IR band at 345 cm-1 and a near-IR (710-850 nm) electronic absorption consisting of a progression in the symmetric stretching mode. The other Se4 isomer has an IR band at 370 cm-1 and a broad, featureless electronic absorption with a maximum at 632 nm. When the products of a microwave discharge in argon seeded with either selenium vapor or H2Se were-condensed, spectra of Se3 were observed in addition to all the Se4 bands. The nu3 fundamental for Se3 was observed at 350 cm-1, and an electronic absorption with 11 peaks assignable to a progression in the symmetric stretching mode extended from 480 to 575 nm.