O 1D quantum yields from O3 photolysis in the near UV region between 305 and 375 nm

Abstract

The formation of O ¹D from the photolysis of ozone has been observed at photolysis wavelengths between 305 and 375 nm and relative quantum yields for O ¹D production have been determined. Ozone was photolyzed using a frequency doubled, optical parametric oscillator. O ¹D was monitored indirectly, using laser induced fluorescence (LIF) detection of vibrationally excited OH as a ‘‘spectroscopic marker’’. Relative O ¹D yields were measured from 305 to 375 nm at 295 K and from 305 to 340 nm at 273 K. The quantum yield decreases between 305 and 325 nm with a temperature dependence in the range between 310 and 325 nm. This is consistent with O ¹D production via both spin-allowed and spin-forbidden processes. Between 325 and 375 nm a constant quantum yield of 0.064±0.006 was obtained suggesting production via an exclusively spin-forbidden process and indicating that absorption takes place to a single excited state which either predissociates, yielding O³P and O₂³Σ⁻, or crosses to another surface before dissociating to produce O ¹D and O₂³Σ⁻.