Formation of ozone by solid state reactions

Abstract

We studied the isotopic composition of ozone formed at low (3–10 K) temperature via O + O₂ solid state reactions using a partially dissociated ¹⁶O/¹⁶O₂ : ¹⁸O/¹⁸O₂ = 1 : 1 mixture. The ozone ice has an isotopic abundance that differs from the statistical one and from gas phase studies. Ozone formation is influenced by the competition of the production of O₂ (O + O or O + O₃) vs. O₃ (O + O₂) and by the energy released in the O + O reaction. The exothermicity of the O + O reaction helps to overcome the barrier of the O + O₂ reaction. Heating the ozone ice past 50 K brings about a transformation from amorphous to crystalline ice. The formation of ozone on water ice yields a blue shift of IR bands, and the yield of formed O₃ increases up to the sample temperature of 100 K. When ¹⁸O/¹⁸O₂ is deposited on H₂¹⁶O ice, formation of ¹⁸O¹⁸O¹⁶O is detected. We propose that the exothermicity of the reaction ¹⁸O + ¹⁸O drives water dissociation (¹⁶O + H₂) followed by ozone formation (¹⁶O + ¹⁸O₂ → ¹⁶O¹⁸O¹⁸O).