Determination of the absolute third-order rate constant for reaction between Cs + O 2 + N 2 by time-resolved atomic resonance absorption spectroscopy

Abstract

The absolute third-order rate constant for the recombination between Cs + O 2 + N 2 was studied by time-resolved atomic resonance absorption spectroscopy following pulsed irradiation of CsCl vapour at elevated temperatures. Cs(6 2S 1 2 ), generated on photolysis, was monitored photoelectrically in absorption in the “single-shot mode” using the spin—orbit resolved Rydberg transition at λ = 455.5 nm (Cs(7p( 2P 3 2 )) ← Cs(6s( 2P 1 2 ))). These photoelectric signals were captured, digitized and stored in a transient recorder, employed in the “A/B” mode, and were transferred directly to a microcomputer for kinetic analysis. Decay profiles for the caesium atom were recorded in the presence of N 2 alone in order to characterize the diffusional loss of the atom (a necessary component of the kinetic study) and in the presence of O 2 + N 2. A diffusion coefficient of D(CsN 2, s.t.p.) = 0.22 ± 0.07 cm 2 s −1 was obtained. The third-order rate constant for the effective single temperature of T = 827 ± 13 K is k(Cs + O 2 + N 2) = (2.01 ± 0.67) × 10 −30 cm 6 molecule −2 s −1. This result is subject to the standard Tröe unimolecular extrapolation to yield the form ln( k rec, 0 (cm 6 molecule −2 s −1)) = (−0.2165 ± 0.00382) (ln T (K)) 2 + (1.0175 ± 0.05) ln( T (K)) − 65.45 ± 0.16. The results are compared with previous kinetic data for Cs + O 2 + Ar obtained from resonance ionization spectroscopy and Cs + O 2 + M obtained in flame environments.