SPIN-FORBIDDEN DISSOCIATION OF OZONE IN THE HUGGINS BANDS

Dissociation of ozone close to room temperature in the Huggins bands b etween 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 evidenc e is seen for the spin-forbidden formation of both of these products i n conjunction with the triplet (ground) state co-fragment, as well as for the dissociation of internally excited ozone molecules to form bot h singlet products in a spin-allowed step. For O(D-1) the ratio of spi n-forbidden to spin-allowed formation increases as the wavelength is i ncreased, and is more pronounced at the peaks in the structured Huggin s bands. The spin-forbidden dynamics are consistent with initial absor ption to a state of B-1(2) symmetry, followed by curve crossing to tri pler states which lead to fragmentation. The implications for the phot ochemistry of tropospheric ozone are briefly discussed. (C) 1998 Elsev ier Science B.V. All rights reserved.