UV Absorption Spectrum and Rate Constant for Self-Reaction of Silyl Radicals

The rate constant of self-reaction of silyl radicals, SiH 3 + SiH 3 → products (1), was measured at 300 K over an extended buffer gas pressure range (1−100 bar, He) using excimer laser pulsed photolysis combined with the transient UV spectroscopy. Silyl radicals were produced in fast reaction of chlorine atoms with silane, Cl + SiH 4 → SiH 3 + HCl. Oxalyl chloride, (COCl) 2, and phosgene, COCl 2, were used as “clean” photodissociation sources of Cl atoms at 193 nm (ArF laser). Silyl radicals were monitored using UV absorption. The absorption cross-sections of SiH 3 radicals are determined using the measured photodepletion of the precursor, (COCl) 2, via its transient absorption at 210 nm. The UV absorption of silyl radical has maximum at 218 nm with the absorption cross-section, σ SiH3 (218 nm) = (2.01 ± 0.11) × 10 -17 cm 2 molecule -1 . No pressure dependence of the overall rate constant of reaction 1 was found over the range 1−100 bar (He). The measured rate constant is: k 1 = (8.25 ± 1.05) × 10 -11 cm 3 molecule -1 s -1 at 300 K. Observed residual UV absorption, tentatively assigned to the dissociation products of the vibrationally excited Si 2 H 6 * molecules formed in reaction 1, is quenched by the buffer gas at 100 bar pressure due to the collisional stabilization of excited disilane molecules.