KINETICS OF SILANE DECOMPOSITION BY ATOMIC AND MOLECULAR NITROGEN METASTABLES

We have studied the reactions of a number of metastable nitrogen species with silane in a discharge-flow reactor. By monitoring the decays in the metastable number densities both as a function of time and as a function of silane number density, we have determined reaction rate coefficients, in units of 10(-11) cm3 molecule-1 S-1, for the following species: N2(A3-SIGMA-u+, upsilon' = 0), 0.84 +/- 0.16; N2(A3-SIGMA-u+, upsilon' = 1), 1.23 +/- 0.24; N2(a'1-SIGMA-u-, upsilon' = 0), 20.7 +/- 5.0; N(2D), 5.9 +/- 1.3; N(2P), 0.09 +/- 0.03; and N(4S), < 0.008. When silane is added to a flow containing only N2(A3-SIGMA-u+), we observe no spectral features of any kind between 220 and 850 nm. Adding silane to a flow of atomic nitrogen excites several atomic lines of silicon, the SiN and SiH bands between 400 and 430 nm, and a continuum extending between 270 and 450 nm, all very weakly. Adding N2(A) to the flow of N(4S) atoms upstream from the silane addition inlet enhances the number densities of N(2P) and N(2D) in the flow and, in addition, the previously observed UV emissions. The UV spectral features are further enhanced when silane is added to the orange afterglow of active nitrogen, which is a mix of all the metastables studied and, in addition, vibrationally excited, ground-electronic-state nitrogen. We suggest that the decomposition of silane is initiated by absorbing several quanta from vibrationally excited nitrogen, followed by H atom stripping in reactions of SiH4 dagger and its fragments with N atoms. The observed excitations result from energy-transfer reactions between the various nitrogen metastables and the silane fragments in the flow.