Thresholds of photolysis of O2 and of formation of O3 from O2 dispersed in solid neon

Abstract

Irradiation of O₂ dispersed in solid Ne with ultraviolet light produced infrared absorption lines of O₃ and emission lines from atomic O (¹D₂ → ³P_1,2), molecular O₂ (A′ ³Δ_u → X ³Σ_g) and radical OH (A ²Σ⁺ → X ²Π_I) in the visible and near-ultraviolet regions. The threshold wavelength for the formation of O₃ was determined to be 200 ± 4 nm, corresponding to energy 6.20 ± 0.12 eV, which is hence the threshold for dissociation of O₂. The thresholds of emission from excited O (¹D₂), O₂ (A′ ³Δ_u) and OH (A ²Σ⁺) were all observed to be 200 ± 4 nm, the same as for the formation of O₃ in this photochemical system. The results indicate that, once O₃ was generated, it was readily photolyzed to produce the long-lived atom O (¹D₂). Further reactions of O (¹D₂) with O₃ produced excited O₂ (A′ ³Δ_u); reaction with water yielded radical OH (A ²Σ⁺). These results enhance our understanding of the evolution of the transformation of oxygen and open a window for the understanding of complicated processes in the solid phase.