On the photodissociation of ozone in the range of 5-9Â eV

The photoabsorption spectrum of ozone in the UV range (5-9 eV) is calculated from a short-time wave packet propagation using six potential energy surfaces obtained from ab initio electronic structure calculations. It is shown that the (unnamed) band around 7 eV, which is immediately adjacent to the intense Hartley band, is primarily due to excitation of three electronic states: 5 1A′ (3 1A1), 6 1A′ (4 1A1), and 4 1A″ (2 1B1). Excitation of the state 8 1A′ (1B2) leads to a broad and intense band starting around 8 eV with a maximum near 9.1 eV. In full accord with the recent experimental study of Brouard et al. [M. Brouard, R. Cireasa, A.P. Clark, G.C. Groenenboom, G. Hancock, S.J. Horrocks, F. Quadrini, G.A.D. Ritchie, C. Vallance, J. Chem. Phys. 125 (2006) 133308], the excitation at 193 nm (6.42 eV) involves at least two states (5 1A′ and 4 1A″) different from the state excited in the Hartley band (3 1A′). The dynamics along the dissociation path is discussed in terms of one-dimensional potential curves. Several avoided crossings among the excited 1A′ as well as the 1A″ states point to a complicated fragmentation process. Although a quantitative analysis of branching ratios is not possible on the basis of the present calculations, we surmise, that in addition to O(3P)+O2(3Σg-) and O(1D) + O2(1Δg), the next higher spin-allowed channel, O(1D)+O2(1Σg+), also is likely to be a major product channel, in agreement with experimental observations.