Dissociation of ozone close to room temperature in the Huggins bands between 310 and 328 nm has been studied by time-of-flight spectroscopy of the resultant O(1D) and O2(a 1Δg) fragments. Clear evidence is seen for the spin-forbidden formation of both of these products in conjunction with the triplet (ground) state co-fragment, as well as for the dissociation of internally excited ozone molecules to form both singlet products in a spin-allowed step. For O(1D) the ratio of spin-forbidden to spin-allowed formation increases as the wavelength is increased, and is more pronounced at the peaks in the structured Huggins bands. The spin-forbidden dynamics are consistent with initial absorption to a state of 1B2 symmetry, followed by curve crossing to triplet states which lead to fragmentation. The implications for the photochemistry of tropospheric ozone are briefly discussed.
