Kinetic study of ground state silicon atoms, Si[3p2(3PJ)], by atomic absorption spectroscopy

Abstract

A direct detailed kinetic study of ground state silicon atoms, Si[3p²(³P_J)] is described. The silicon atoms were generated by repetitive pulsed irradiation of SiCl₄ and monitored photoelectrically using resonance line absorption coupled with signal averaging. Particular attention is directed towards investigation of the kinetic behaviour of the close lying individual spin orbit states by optical isolation of the appropriate resonance transitions during the time-resolved measurements. Thus we have employed for Si(3³p₀). λ= 251.43 nm ( 4³P₁â†� 3³P₀), for Si(3³P₁), λ= 250.69 nm (4³P₂â†� 3³P₁) and, for Si(3³P₂), λ= 251.61 nm (4³P₂â†� 3³P₂). Kinetic measurements were also made on a group of lines centred on λ= 251.6 nm. Detailed kinetic studies with a range of SiCl₄+ He mixtures clearly showed the maintenance of a Boltzmann equilibrium between the spin orbit states during the measurements on the decays of the transient atoms. We report absolute second-order rate constants for the chemical reaction of Si(3³P_J) with O₂ and N₂O, namely, kO₂= 2.7 ± 0.3 × 10^–10 and KN₂O= 1.9 ± 0.2 × 10^–10 cm³ molecule^–1s^–1(300 K). These rate data are compared with analogous data for C(2³P_J), Ge(4³P_J), Sn(5³P₀) and Pb(6³P₀), and are discussed within the context of the nature of the appropriate potential surfaces resulting from symmetry arguments based on the weak spin orbit coupling approximation for light atom-molecule collisions and (J, Ω) coupling for heavy atom–molecule collisions.