Kinetic Studies of the Reactions of O₂(b¹Σ_g⁺) with Several Atmospheric Molecules

Thermal rate coefficients for the removal (reaction + quenching) of O₂(¹Σ_g⁺) by collision with several atmospheric molecules were determined to be as follows:  O₃, k₃(210−370 K) = (3.63 ± 0.86) × 10^-11 exp((−115 ± 66)/T); H₂O, k₄(250−370 K) = (4.52 ± 2.14) × 10^-12 exp((89 ± 210)/T); N₂, k₅(210−370 K) = (2.03 ± 0.30) × 10^-15 exp((37 ± 40)/T); CO₂, k₆(298 K) = (3.39 ± 0.36) × 10^-13; CH₄, k₇(298 K) = (1.08 ± 0.11) × 10^-13; CO, k₈(298 K) = (3.74 ± 0.87) × 10^-15; all units in cm³ molecule^-1 s^-1. O₂(¹Σ_g⁺) was produced by directly exciting ground-state O₂(³Σ_g^-) with a 762 nm pulsed dye laser. The reaction of O₂(¹Σ_g⁺) with O₃ was used to produce O(³P), and temporal profiles of O(³P) were measured using VUV atomic resonance fluorescence in the presence of the reactant to determine the rate coefficients for removal of O₂(¹Σ_g⁺). Our results are compared with previous values, where available, and the overall trend in the O₂(¹Σ_g⁺) removal rate coefficients and the atmospheric implications of these rate coefficients are discussed. Additionally, an upper limit for the branching ratio of O₂(¹Σ_g⁺) + CO to give O(³P) + CO₂ was determined to be ≤0.2% and this reaction channel is shown to be of negligible importance in the atmosphere.