Collisional behaviour of atomic silicon in specific electronic states, Si(3 3PJ, 3 1D2, 3 1S0), with molecular fluorine studied by time-resolved atomic resonance absorption spectroscopy

Abstract

We present a kinetic study of atomic silicon in the three low-lying electronic states arising from the overall 3p² ground-state configuration, namely Si(3 ³P_J)(0 eV), Si(3 ¹D₂)(0.781 eV) and Si(3 ¹S₀)(1.909 eV). Si(3 ³P_J, 3 ¹D₂ and 3 ¹S₀) were generated by the repetitive pulsed irradiation of SiCl₄ in the presence of an excess of helium buffer gas in a slow-flow system, kinetically equivalent to a static system. The photochemically generated transient atoms were monitored photoelectrically by time-resolved resonance absorption at λ= 251.6 nm [Si(4 ³P_Jâ†� 3 ³P_J)], λ= 288.16 nm [Si(4 ¹P₁â†� 3 ¹D₂)] and λ= 390.53 nm [Si(4 ¹P₁â†� 3 ¹S₀)] using pre-trigger photomultiplier gating with signal averaging. The decays of these atoms were investigated in the presence of molecular fluorine, leading to the following absolute second-order rate constants (k₂): [graphic omitted]

The result for Si(3 ³P_J)+ F₂ is compared with data derived from previous measurements carried out at 600 K on a flow system, and the data as a whole are compared with the results of earlier kinetic studies on Si(3 ³P_J, 3 ¹D₂, 3 ¹S₀)+ Cl₂. Reaction pathways to defined product states of SiF + F are considered in terms of symmetry arguments based on the weak spin–orbit coupling approximation. Discussion is also presented on the use of time-resolved spontaneous emission from product states of SiF + F as spectroscopic markers for kinetic investigations of defined electronic states of atomic silicon and the feasibility of investigating stimulated emission from SiF(a⁴Σ)—SiF(A²Σ⁺)+hν in the 1.4 µm region in the pulsed mode following the reaction of the electronically excited Si(3 ¹D₂) and Si(3 ¹S₀) with F₂.