Ion Imaging Study of NO3 Radical Photodissociation Dynamics: Characterization of Multiple Reaction Pathways

The photodissociation of NO3 has been studied using velocity map ion imaging. Measurements of the NO2 + O channel reveal statistical branching ratios of the O(P-3(J)) fine-structure states, isotropic angular distributions, and low product translational energy consistent With barrierless dissociation along the:ground state potential surface. There is clear evidence for two distinct pathways to the formation of NO + O-2 products. The dominant pathway (> 70% yield) is characterized by vibrationally excited O-2((3)Sigma(-)(g), nu = 5-10) and rotationally cold NO((2)Pi), while the second pathway is characterized by O-2((3)Sigma(-)(g), nu = 0-4) and rotationally hotter NO((2)Pi) fragments. We speculate the first pathway has many similarities to the roaming dynamics recently amplicated in several systems. The rotational angular momentum of the molecular fragments is positively correlated for this channel, suggesting geometric constraints in the dissociation. The second pathway results, in almost exclusive formation of NO((2)Pi, nu = 0). Although product state correlations support dissociation via an as yet unidentified three-center transition state, theoretical confirmation is needed.