Laser spectrometry and kinetics of selected elementary reactions of the acetonyl radical

Abstract

The laser induced fluorescence excitation spectrum (LIF) and the ultraviolet absorption spectrum (TA) of the acetonyl radical (CH₃C(O)CH₂) were remeasured by using the time-resolved fast discharge flow (DF) and laser flash photolysis (LP) experimental techniques (T = 298 K). The absorption cross section of σ(acetonyl, 207 nm) = (3.16 ± 0.61) × 10⁻¹⁸ cm² molecule⁻¹ was determined calibrated against the acetyl-peroxyl radical (CH₃C(O)O₂) in LP/TA measurements. The kinetics of the reactions of CH₃C(O)CH₂ with the open shell reaction partners O₂ (1), NO (2), NO₂ (3) and H (4) were studied by using the DF method with LIF detection of the acetonyl radical at 298 ± 1 K and 2.85 ± 0.05 mbar He pressure. The rate constants for the overall reactions were determined in units of cm³ molecule⁻¹ s⁻¹ to be k₁ = (3.49 ± 0.51) × 10⁻¹³, k₂ = (1.04 ± 0.19) × 10⁻¹¹, k₃ = (3.25 ± 0.65) × 10⁻¹¹ and k₄ ≥ 3 × 10⁻¹⁰ with 2σ accuracy given. The acetonyl radical was found to react similarly to alkyl radicals by comparison with literature results. A reduced reactivity was observed toward O₂ and NO that might be attributed to the resonance stabilisation of the acetonyl radical. No such effect was observed for the NO₂ and H atom reactions.