Spin-forbidden dissociation of ozone in the Huggins bands Original Research Article

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.