Product energy partitioning in the unimolecular decomposition of vibrationally and rotationally state‐selected hydrogen peroxide

Infrared-optical double resonance prepares HOOH molecules in single rotational levels of the 6-nu(OH), 5-nu(OH) + nu(OOH), 5-nu(OH) + nu(OO), and 4-nu(OH) + nu(OH), vibrational states which range from 3 to 2287 cm-1 of excess energy above the unimolecular dissociation threshold. Laser-induced fluorescence probes the nascent OH rotational state distributions from the decomposition of rovibrationally selected reactants. The nascent rotational state distributions reveal that both OH spin-orbit states can be populated by the decomposition of a single molecule and hence that electronic angular momentum is not conserved throughout the dissociation process. The product state distributions from reactants excited to the 6-nu(OH) and 4-nu(OH) + nu(OH), vibrational levels are generally in good agreement with the predictions of phase-space theory provided electronic angular momentum is treated statistically. Reactants decomposing from single rotational states in the 5-nu(OH) + nu(OOH) combination level (and to a lesser extent the 5-nu(OH) + nu(OO) level) show product state distributions which are systematically colder than phase-space theory predictions. This observation indicates that energy redistribution in vibrationally excited HOOH is not complete on the time scale of unimolecular decomposition.