The relative quantum yields of O2(a1Δg) from the photolysis of ozone have been measured at 227(¿2)K over the wavelength range 300 nm≥&lgr;≥322 nm, 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(1D) yields which show a shift in the fall--off curve to shorter wavelengths at low temperature. For &lgr;>309 nm, the yield at 227K falls more rapidly than that at 298K, confirming that internal energy mediated dissociation of ozone provides the major source of O2(a1Δg) at wavelengths just beyond the 310 nm threshold for the spin allowed production of the two singlet products. However, the yields of O2(a1Δg) at 227K and 298K were found to be approximately equal for photolysis wavelengths &lgr;≥320 nm, and substantially larger than O(1D) 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 O2(a1Δg) with a quantum yield of &PHgr;≈0.1 at wavelengths near to 320 nm. ¿ American Geophysical Union 1995