THE RELATIVE QUANTUM YIELDS OF O-2(A(1)DELTA(G)) FROM THE PHOTOLYSIS OF OZONE AT 227K

The relative quantum yields of O-2(a(1) Delta(g)) from the photolysis of ozone have been measured at 227(+/-2)K over the wavelength range 300nm greater than or equal to lambda greater than or equal to 322nm, and are compared to those measured previously at 298K [Ball et al., 1993]. The yields at the two temperatures show the same initial wavelength dependence in the fall-off region, in contrast to literature measurements of the O)(D-1) yields which show a shift;in the fall-off curve to shorter wavelengths at low temperature. For lambda > 309nm, the yield at 227K falls more rapidly than that at 298K, confirming that internal energy mediated dissociation of ozone provides the major source of O-2(a(1) Delta(g)) at wavelengths just beyond the 310nm threshold for the spin allowed production, of the two singlet products. However, the yields of O-2(a(1) Delta(g)) at 227K and 298K were found to be approximately equal for photolysis wavelengths lambda greater than or equal to 320nm, and substantially larger than O(D-1) yields predicted from modelling currently available for the photolysis of vibrationally excited ozone. These results suggest the existence of a spin forbidden dissociation channel for O-2(a(1) Delta(g)) with a quantum yield of Phi = 0.1 at wavelengths near to 320nm.