Photodissociation of ozone in the Chappuis band. II. Time-dependent wave-packet calculations and interpretation of diffuse vibrational structures

We present time-dependent wave-packet calculations describing the photodissociation of ozone in the Chappuis band, which evolves in the two lowest states of ¹A″ symmetry. The calculations are performed in the diabatic representation and include the coupling between the two relevant states. All three nuclear degrees of freedom are taken into account. The two potential-energy surfaces, the coupling potential, and the two transition-dipole-moment functions with the electronic ground state have been calculated previously by ab initio methods [Woywod et al., J. Chem. Phys. 107, 7282 (1997)]. The coupling between the two diabatic states is exceedingly strong, resulting in very fast dissociation into O+O₂ on the time scale of only one symmetric stretch period. A small portion of the initially created wave packet is temporarily trapped leading to three tiny recurrences, which reflect basically symmetric stretch motion plus some amount of bending motion. The experimentally observed diffuse vibrational structures superimposed to the broad absorption spectrum are satisfactorily reproduced and discussed both in the time-independent and the time-dependent picture of spectroscopy. In view of the very short lifetime in the excited states, the correspondingly large widths of the diffuse structures, and the participation of all three vibrational modes we conclude that an unique assignment in terms of three quantum numbers is not possible. The main structures are due to symmetric stretch excitation, but bending and even asymmetric stretch motion are also involved. A one-state model, in which only the upper (bound) adiabatic potential is employed, provides a qualitatively correct explanation of the absorption spectrum and the diffuse structures.