The near-uv photolysis of ozone: quantum yields of O(1D) between 305 and 329 nm at temperatures from 227–298 K, and the room temperature quantum yield of O(3P2) between 303 and 310 nm, measured by resonance enhanced multiphoton ionisation

Abstract

Quantum yields Φ have been measured for the O(¹D) fragment from the photolysis of ozone between 305 and 329 nm at temperatures of 298, 273, 247 and 227 K. Relative yield measurements of the atomic fragment were made by REMPI, and placed on an absolute scale by comparison with published quantum yields at 308 nm. The results confirm the existence of the long wavelength “tail” for O(¹D) production beyond the 310 nm thermodynamic threshold for its formation in a spin allowed step with O₂(a¹Δ_g) as the cofragment. Contributions from both photodissociation of internally excited ozone and spin forbidden processes are apparent from the temperature and wavelength dependences of Φ. These results give support to the recently recommended values of the quantum yields in this wavelength and temperature region. Measurements over the structured Huggins band near 319 nm show evidence of an anticorrelation between the O(¹D) yield and the absorption cross section, but the effect is not large enough to make significant error in the continuous function used to parametrise the quantum yield in this region. Measurements of the quantum yield of the O(³P₂) fragment between 303 and 310 nm indicate that the short wavelength limiting value of the O(¹D) quantum yield at room temperature lies between 0.85 and 0.9.