Laser induced fluorescence studies of the reactions of O(1D2) with N2, O2, N2O, CH4, H2, CO2, Ar, Kr and n-C4H10

Abstract

A laser flash photolysis–laser-induced fluorescence (LIF) technique has been used to study the kinetics of the reactions of electronically excited oxygen atoms, O(¹D₂), with N₂, O₂, N₂O, CH₄, H₂, CO₂, Ar, Kr and n-C₄H₁₀ over the temperature range 195–673 K. The majority of studies employed direct detection of O(¹D₂) atoms using vacuum ultraviolet LIF at 115.2 nm, whereas some studies employed LIF detection of OH generated from reaction of O(¹D₂) with a H atom donor species as a marker for O(¹D₂). The bimolecular rate coefficient for reaction with N₂ (k_N2) is well described by the Arrhenius expression k_N2 = (2.2 ± 0.3) × 10⁻¹¹exp{(118 ± 21)/T} (95% confidence level), in good agreement with two other new studies reported in this issue, but giving significantly higher values of k_N2 than previously measured, with important implications for production rates of OH and NO radicals in the atmosphere. At 295 K the following rate coefficients were obtained (in units of cm³ molecule⁻¹ s⁻¹, 95% confidence level including estimated systematic errors): k_N2 = (3.06 ± 0.25) × 10⁻¹¹, k_O2 = (3.8 ± 0.4) × 10⁻¹¹, k_N2O = (1.07 ± 0.1) × 10⁻¹⁰, k_CH4 = (1.4 ± 0.2) × 10⁻¹⁰, k_H2 = (1.5 ± 0.1) × 10⁻¹⁰, k_CO2 = (1.4 ± 0.1) × 10⁻¹⁰, k_Ar = (8 ± 3) × 10⁻¹³, k_Kr = (9 ± 1) × 10⁻¹² and k_n-C4H10 = (4.55 ± 0.2) × 10⁻¹⁰, in good agreement with the new studies reported in this issue, and with previous measurements, where available. An analysis of the correlation between the cross-section for O(¹D₂) removal and the ionisation potential of the collision partner suggests at least two mechanisms operate for the removal of O(¹D₂).