Measurement of absolute rate data for the reaction of ground state atomic silicon, Si(33PJ), with halogenated olefinic and aromatic compounds by time‐resolved atomic resonance absorption spectroscopy

Abstract

AbstractWe present a kinetic study of the reaction of ground state silicon atoms with halogenated unsaturated organic compounds (R). Si(33PJ) was generated by the repetitive pulsed irradiation of SiCl4 in the presence of excess helium buffer gas and the reactant R in a slow flow system, kinetically equivalent to a static system. The ground state atom was monitored by time‐resolved atomic resonance absorption spectroscopy at λ = 252 nm [Si(43PJ) ← Si(33PJ)] on time scales by which the optically metastable tates,Si(31D2) and Si(31S0) had relaxed to the 3P state, using signal averaging methods. Computerized fitting of the resulting atomic decay traces in the presence of the various reactants, R, yielded the following new body of absolute second‐order rate constants (kR, T = 300 K, errors = 2sigma;): R kR/cm3 molecule−1 s−1 C2F4 1.6 ± 0.2 × 10−10 C2Cl4 9.9 ± 1.7 × 10−10 CH2CF2 4.0 ± 0.6 × 10−10 CHClCCl2 7.0 ± 1.1 × 10−10 CF3CHCH2 4.6 ± 0.5 × 10−10 C6H6 4.4 ± 1.0 times; 10−10 C6F6 4.4 ± 0.6 × 10−10 C6HF5 4.6 ± 1.3 × 10−10 C6H2F4 3.9 ± 0.8 × 10−10 C6F5—CF3 5.1 ± 0.6 × 10−10 These data are compared, where appropriate, with analogous data for unsaturated hydrocarbon organic compounds. They are also discussed within the general context of nuclear recoil measurements involving 31Si.