ELECTRONIC ABSORPTION-SPECTRA OF SI-N AND SI-N(-) (N=2-4) IN NEON MATRICES

Electronic absorption spectra of silicon molecules Si-n and Si-n(-) (n = 2-4) in 5 K neon matrices have been observed. The approach is based on mass-selection and codeposition with neon. The neutral species bec ome apparent after photodetachment. The band systems detected are assi gned using available calculations and photoelectron spectra. In the ca se of Si-3 (C-2v), electronic transitions from the X (1)A(1) ground st ate to the excited electronic states B-1(1), (1)A(1), B-1(1), and B-1( 2) have been identified. Their 0(0)(0) bands are at 778.9, 579.7, 522. 3, and 388.3 nm, respectively. Two band systems, with origin bands at 925.3 and 466.6 nm, are assigned to the B-1(3u) <-- X (1)A(g) and B-1( 1u) <-- X (1)A(g) transitions of Si-4 (D-2h). Two known electronic tra nsitions are obtained for Si-2, but a reported band system with origin at 288.3 nm cannot be due to this molecule. The following electronic transitions were detected for the anions: Si-2(-), (2) Pi(u) <-- X (2) Sigma(g)(+); Si-3(-) (C-2v), (2)A(1) <-- X (2)A(1); Si-4(-) (D-2h), B -2(1u) <-- X B-2(2g), with origin bands at 432.7, 1036.7, and 872.6 nm . Vibrational frequencies of several totally symmetric modes could be inferred for the studied species in the electronic excited states.