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

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 2011-04, Vol.115 (15), p.3218-3226
• Main Authors: Grubb, Michael P, Warter, Michelle L, Johnson, Kurt M, North, Simon W
• Format: Article
• Language: English
• Subjects: A: Dynamics, Clusters, Excited States; Free Radicals - chemistry; Ions - chemistry; Nitrates - chemistry; Nitric Oxide - chemistry; Oxygen - chemistry; Photochemical Processes; Thermodynamics
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp200110e

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(3P 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 + O2 products. The dominant pathway (>70% yield) is characterized by vibrationally excited O2(3Σg −, v = 5−10) and rotationally cold NO(2Π), while the second pathway is characterized by O2(3Σg −, v = 0−4) and rotationally hotter NO(2Π) fragments. We speculate the first pathway has many similarities to the “roaming” dynamics recently implicated 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(2Π, v = 0). Although product state correlations support dissociation via an as yet unidentified three-center transition state, theoretical confirmation is needed.