DISSOCIATION OF HIGHLY EXCITED NO2 INDUCED BY COLLISIONS WITH AR, CO, AND O-2

The gas-phase collision-induced dissociation (CID) of highly excited, mixed (2)A(1)/B-2(2) states of NO2 with Ar, CO, and O-2 is studied in crossed beams experiments with state-resolved detection of products. Both the internal and translational energy of the reactants are varied independently. The state-specific relative yield of the NO product as a function of the initial NO2 excitation is reported for excitation energies hv from dissociation threshold D-0 to D-0 - hv = 1000 cm(-1). The relative collision energies are 750-2400 cm(-1) The structure of the CID yield spectrum is similar to that observed in the fluorescence excitation spectrum of NO2, and the scaling of the collisional energy transfer efficiency can be described by an exponential decay law. NO is detected using laser ionization, and rotational and spin-orbit distributions are determined. CID is described fairly well by assuming a unimolecular decomposition (UMD) of NO2, collisionally excited to a range of excess energies above D-0 with excitation probability determined by the exponential gap law. The average energy transferred per activating collision is in the range 110-310 cm(-1), dependent on both the relative collision energy and the nature of the collider. Higher product spin-orbit excitations are observed with CO and O-2 than with Ar which suggests a stronger exit-channel interaction with these colliders.