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

Abstract

The rate constant of self-reaction of silyl radicals, SiH 3 + SiH 3 f 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 f 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.

Time-resolved cavity ringdown study of the Si and SiH3 surface reaction probability during plasma deposition of a-Si:H at different substrate temperatures

“…2. SiH 3 has unambiguously been identified in our plasma 35,63 from the good agreement with the normalized absorption spectra of SiH 3 reported by Baklanov and Krasnoperov 64 and Lightfoot et al 65 ( Fig. 2) as well as from the good agreement with threshold ionization mass spectrometry measurements of SiH 3 .…”

“…60 Si has been measured from the atomic line spectrum of the Si 4s 3 P 0,1,2 ← 3p 2 3 P 0,1,2 transition at ϳ251 nm, 66 which lies superimposed on the SiH 3 spectrum, as is shown in the inset of In this paper, both Si and SiH 3 are detected around 250.7 nm: Si at the 4s 3 P 2 ← 3p 2 3 P 1 transition at 250.69 nm with peak absorption cross section of 4.17 ϫ 10 −17 m 2 , 66 and SiH 3 at the underlying broadband spectrum with an absorption cross section of ϳ4.9ϫ 10 −22 m 2 , as reported recently by Baklanov and Krasnoperov. 64 This new and more accurate absorption cross section of SiH 3 differs only slightly from the previously used absorption cross section of Lightfoot et al 65 …”

Kinetics of the Self-Reaction of C2H5 Radicals

“…Reaction 1 was studied by laser photolysis/photoionization mass spectrometry. A relatively novel approach based on the method developed by Baklanov and Krasnoperov 11,12 was used to photolytically produce ethyl radicals in known concentrations: 193-nm laser photolysis of oxalyl chloride ((CClO) 2 ), producing Cl atoms, followed by a fast reaction of Cl with ethane. The experimental method was first validated by determining the rate constants of the wellstudied reaction of recombination of methyl radicals.…”

Excitation energies, photoionization cross sections, and asymmetry parameters of the methyl and silyl radicals

“…Much less spectroscopic investigation has been made of silyl radical, even though it is an important intermediate in the mechanism of the gas-phase chemical transformations of silicon molecules. 11 In fact, to the best of our knowledge, photoionization cross sections of SiH 3 have not been reported to date.…”