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

Using pulsed laser photolysis (PLP) and laser-induced fluorescence (LIF) we have studied the formation of O2(X3Σg-) 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(X3Σg-) in high vibrational levels is formed primarily as a product of the reaction between O(1D) atoms and O3: O(1D)+O3→2 O2(X3Σg-, v). In a large excess of N2, the O(1D) atoms are quenched and one only observes the O2(X3Σg-) molecules created by direct photolysis in the ‘triplet channel’: O3+hν (λ=266 nm)→O2(X3Σg-, v)+O(3P). Employing LIF in the (0, v) and (2, v) bands of the O2 (B 3Σu-–X3Σg-) 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(X3Σg-, 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(X3Σg-) and the implications of the results for atmospheric chemistry are discussed.