SPECTRA AND STRUCTURES OF THE FREE HSiCl AND HSiBr RADICALS

Abstract

Intense spectra of HSiCl and HSiBr in the region 6000 to 4100 Å have been obtained in the flash photolysis of SiH₃Cl and SiH₃Br, both in absorption and in fluorescence. They consist of progressions of bands with very wide K structures and very narrow J structures. A detailed fine structure analysis of these bands has been carried out and the geometrical structure of the molecules in both the upper and the lower states has been established. For the lower state, probably the ground state of HSiCl, it is found that and similarly for HSiBr In the excited states the angles are appreciably larger (see Table XI).A striking feature of the band structure in both HSiCl and HSiBr is the occurrence of branches of subbands with ΔK = ± 2, in addition to those with ΔK = ± 1 and 0, and furthermore, the presence of a subband with K = 0 in the branch with ΔK = 0. These anomalies can be accounted for by the assumption that the electronic transition is a triplet–singlet transition, more specifically ³A″–¹A′ (or possibly ¹A′–³A″). However, no triplet splitting has been resolved in the spectrum.