Photodissociation dynamics and potential surfaces of hydrogen peroxide

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Abstract
The dynamics of photodissociation of H2O2 from low lying excited electronic states was studied by classical trajectory calculations. Potential energy functions were constructed for both the ground and two excited states of H2O2. Parameters in the ground state function were chosen to fit vibrational frequencies, potential barriers, and the equilibrium structure. Parameters in the excited state functions were chosen to fit the observed OH rotational state distribution and to be consistent with the electronic spectrum. The moderate rotational excitation of the OH radicals is mostly explained by the fact that the repulsive O–O force exerts a small torque around the center of mass of the OH radicals. The results at 5.00 and 6.42 eV cannot both be fit with the same potential surface suggesting that at least two if not all three of the low lying excited states predicted by Evleth play a role in the electronic absorption. The importance sampling technique was used to weight the initial conditions with the Wigner distribution. As a consequence only a modest (103) number of trajectories were needed to generate a representative rotational distribution. One useful result which may be general is that the rotational distributions resulting from a given surface were little dependent on the photon energy but that use of a steeper potential gave rise to more rotational excitation.