Formation and relaxation of O2(X3Σg-) in high vibrational levels (18⩽⩽23) in the photolysis of O3 at 266 nm

Abstract

Using pulsed laser photolysis (PLP) and laser-induced fluorescence (LIF) we have studied the formation of O₂(X³Σ_g^-) in high vibrational levels when O₃ is photolysed at 266 nm. Experiments have been performed in both Ar and N₂ diluents. In the former, O₂(X³Σ_g^-) in high vibrational levels is formed primarily as a product of the reaction between O(¹D) atoms and O₃: O(¹D)+O₃→2 O₂(X³Σ_g^-, v). In a large excess of N₂, the O(¹D) atoms are quenched and one only observes the O₂(X³Σ_g^-) molecules created by direct photolysis in the ‘triplet channel’: O₃+hν (λ=266 nm)→O₂(X³Σ_g^-, v)+O(³P). Employing LIF in the (0, v) and (2, v) bands of the O₂ (B ³Σ_u^-–X³Σ_g^-) system, we have characterised the nascent vibrational distributions from both these processes for 18⩽v⩽23. In addition, by observing how the population in specific vibrational levels changes with time, we have determined rate constants for vibrational relaxation of O₂(X³Σ_g^-, v=21 and 22) with He, O₂, N₂, CO₂, N₂O and CH₄. The results are compared with those obtained in other studies for relaxation from the same and other levels of O₂(X³Σ_g^-) and the implications of the results for atmospheric chemistry are discussed.