Spin-forbidden dissociation of ozone in the Huggins bands

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(D-1) and O-2(a(1)Delta(g)) 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(D-1) 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 B-1(2) symmetry, followed by curve crossing to tripler states which lead to fragmentation. The implications for the photochemistry of tropospheric ozone are briefly discussed. (C) 1998 Elsevier Science B.V. All rights reserved.