Kinetics of SiF(X2Πr) by time-resolved molecular resonance absorption spectroscopy following the reaction of Si(3 3PJ, 3 1D2, 3 1S0), generated by pulsed irradiation, with fluorinated compounds

Abstract

We present an investigation of the ground and first excited states of SiF(X²Π_r and A²Σ⁺) leading to the first measurements of absolute second-order rate constants for this molecule. SiF(X²Π_r) was produced from the reaction of Si(3³P_J, 3¹D₂, 3¹S₀) with molecules of the type RF, generated by the repetitive pulsed irradiation of SiCl₄ in the presence of an excess of helium buffer gas in a slow-flow system. SiF(X²Π_r) was monitored by time-resolved molecular resonance absorption at λ= 436.8 nm [SiF(A ²Σ⁺)â†� SiF(X²Π_r), (0,0)] using signal-averaging techniques. The growth of SiF derived from the absorption profile measured in the presence of F₂, SiF₄ and SF₆ was in accord with previously reported rate data for the removal of Si(3 ³P_J), Si(3 ¹D₂) and Si(3 ¹S₀). The decay components of the SiF(X²Π_r) derived from the profiles yielded the following absolute second-order rate constants for reaction with RF: [graphic omitted] F-atom abstraction being highly exothermic in all cases and demonstrating similar reactivity to atomic silicon itself. We also report time-resolved chemiluminescence measurements on SiF(A²Σ⁺→X²Π_r) at λ= 436.8 nm using photon-counting techniques. The emission decay profiles are consistent with the removal of atomic silicon and indicate the correlation of SiF(A–X) chemiluminescence as a spectroscopic marker technique for kinetic studies of atomic silicon in specific electronic states. Finally, from the results of the present investigation and previously reported absolute rate data for the removal of atomic silicon, we suggest the design for the future construction of a pulsed molecular electronic chemical laser based on the transition SiF(a⁴Σ^–)→ SiF(A²Σ⁺)+hν(1.4 µm) generated by the reaction of excited states of Si(3 ¹D₂ and 3 ¹S₀) with F₂.