UV absorption spectrum and rate constant for self-reaction of silyl radicals

The rate constant of self-reaction of silyl radicals, SiH3 + SiH3 --> produ cts (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 tran sient UV spectroscopy. Silyl radicals were produced in fast reaction of chl orine atoms with silane, Cl + SiH4 --> SiH3 + HCl. Oxalyl chloride, (COCl)( 2), and phosgene, COCl2, were used as "clean" photodissociation sources of Cl atoms at 193 nm (ArF laser). Silyl radicals were monitored using UV abso rption. The absorption cross-sections of SiH3 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 21 8 nm with the absorption cross-section, sigma (SiH3)(218 nm) = (2.01 +/- 0. 11) x 10(-17) cm(2) molecule(-1). No pressure dependence of the overall rat e constant of reaction 1 was found over the range 1-100 bar (He). The measu red rate constant is: k(1) = (8.25 +/- 1.05) x 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 Si2H6* molecules formed in reaction 1, is quenched by the buffer gas at 100 bar pressure due to th e collisional stabilization of excited disilane molecules.