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 30 0nm greater than or equal to lambda greater than or equal to 322nm, an d 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 measurem ents 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 interna l energy mediated dissociation of ozone provides the major source of O -2(a(1) Delta(g)) at wavelengths just beyond the 310nm threshold for t he 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 approxi mately equal for photolysis wavelengths lambda greater than or equal t o 320nm, and substantially larger than O(D-1) yields predicted from mo delling currently available for the photolysis of vibrationally excite d ozone. These results suggest the existence of a spin forbidden disso ciation channel for O-2(a(1) Delta(g)) with a quantum yield of Phi = 0 .1 at wavelengths near to 320nm.