Quantum mechanical calculation for photodissociation of hydrogen peroxide

Quantum dynamics calculations are carried out to study ultraviolet (UV) photodissociation of H₂O₂ at a photon energy of 248 nm. The photodissociation process of hydrogen peroxide is simulated by the standard two-surface model using an ab initio ground potential energy surface and a simple empirical excited surface. The time-dependent approach is employed in quantum dynamics calculations due to the short-time nature of the dissociation process. In this calculation, two high-frequency OH stretching modes are kept frozen but the remaining four degrees of freedom are treated fully quantum mechanically. The quantum calculation fully utilizes the symmetry properties of the system and each symmetry block is computed separately. The computed rotational state distribution of the OH fragments is in qualitative agreement with the classical calculation of Bersohn and Shapiro, with most of the excess energy being carried away by the relative translational motion of the OH fragments. The effect of torsional mode on the rotational state distribution is investigated by calculating the Franck-Condon factors of photodissociation using torsionally excited bound state wave function. Our calculated rotational state distribution, averaged over contributions of two parity-splitting states, is found to be in good agreement with that observed in experiment.