The formation of Se-2(-): A new resonance Raman feature in the photochemistry of zeolite-encapsulated selenium

This Raman spectroscopic study on selenium incorporated in Nd-Y zeolite presents new aspects of the photochemistry of selenium. The formation of the Se-2(-) radical anion has been established from its resonance Raman spectrum, consisting of ten almost equidistant bands between 328 and 3220 cm(-1) on the low-energy side of the 476.24-nm laser excitation line. The derived spectroscopic constants of the electronic ground state are omega(0) = 328 cm(-1) and chi(0) omega(0) = 0.71 cm(-1). Another broad band at 260 cm(-1) resembles features in the Raman spectra of amorphous selenium and selenium chain structures encapsulated in zeolites. Continuous irradiation at sufficiently high laser power levels leads to depletion of the 260 cm(-1) band and a simultaneous enhancement of the Se-2(-) bands. These observations are discussed with respect to the defect states conventionally invoked for reversible photoinduced changes in amorphous selenium.