Laboratory Study of O(1S) Formation Process in the Photolysis of O3 and its Atmospheric Implications

A high-sensitive technique to detect O(¹S) atoms using vacuum ultraviolet laser-induced fluorescence (VUV-LIF) spectroscopy has been applied to study the O(¹S) production process from the UV photodissociation of O₃, N₂O, and H₂O₂. The quantum yields for O(¹S) formation from O₃ photolysis at 215 and 220 nm are determined to be (1.4 ± 0.4) × 10⁻⁴ and (5 ± 3) × 10⁻⁵, respectively. Based on thermochemical considerations, the O(¹S) formation from O₃ photolysis at 215 and 220 nm is attributed to a spin-forbidden process of O(¹S)+O₂(X³Σ_g ⁻). Analysis of the Doppler profile of O(¹S) produced from O₃ photolysis at 193 nm also indicates that the O(¹S) atoms are produced from the spin-forbidden process. In the photolysis of N₂O and H₂O₂ at 193 nm, no discernible signal of O(¹S) atoms has been detected. The upper limit values of the quantum yields for O(¹S) production from N₂O and H₂O₂ photolysis at 193 nm are estimated to be 8 × 10⁻⁵ and 3 × 10⁻⁵, respectively. Using the experimental results, the impact of the O(¹S) formation from O₃ photolysis on the atmospheric OH radical formation through the reaction of O(¹S)+H₂O has been estimated. The calculated results show that the contribution of the O(¹S)+H₂O reaction to the OH production rate is ∼2% of that of the O(¹D)+H₂O reaction at 30 km altitude in mid-latitude. Implications of the present laboratory experimental results for the terrestrial airglow of O(¹S) at 557.7 nm have also been discussed.