Study of vibrational energy localization and redistribution in hydrogen peroxide H2O2 at low energy

Vibrational energy localization and/or redistribution in hydrogen peroxide H2O2 is studied at about 4000 cm(-1) above the quantum mechanical ground state using the ab initio potential energy surface of Koput, Carter, and Handy [J. Phys. Chem. A 102, 6325 (1998)]. In this work, the recently derived canonical perturbation procedure for floppy molecules serves two purposes. First, from the quantum mechanical point of view, it is shown that the energies of the lowest 130 states are reproduced with an average error smaller than 1.5 cm(-1) by a two-dimensional Hamiltonian, which is a function of the torsion and OO-stretch coordinates and momenta, while the other four degrees of freedom contribute only through powers of good quantum numbers. Moreover, the canonical perturbation procedure is also used in classical mechanics calculations, in order to define meaningful local modes, for which the ingoing and outgoing energy flows are monitored. Almost all the individual trajectories launched on the ab initio surface display the same behavior, that is, the superposition of (a) rapid (few hundreds of femtoseconds) and quasiperiodic energy exchanges between the two OH stretches and between the torsion and OO-stretch, and (b) slower (few to several picoseconds) but erratic-looking energy flows between all degrees of freedom. When averaging over large numbers of trajectories with the same local mode energies at time t=0, one observes instead a smooth and irreversible energy flow between all degrees of freedom, which usually thermalize in the range of several tens of picoseconds, that is, on time scales larger than the 5 ps period associated with the quantum density of states.