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"Roaming in the Dark: Multistate Dynamics in the Photochemistry of the Nitrate Radical"

Simon North
Department of Chemistry
Texas A&M University


It has been over a century since the nitrate radical, NO3, was first observed by optical absorption [J. Chappuis, Ann. Sci. Ec. Norm. Sup., 1882, 11, 137] but the mechanism of NO and O2 production through the visible photolysis has long proven elusive. Recent ion imaging studies and ab initio calculations have suggested that two distinct pathways are responsible for molecular products and that both pathways involve ‘roaming dynamics’ on the ‘dark’ excited electronic state. Thus, the NO3 --> NO + O2 reaction proceeds in the absence of a traditional transition state. New vector correlation and Λ doublet propensity measurements have been performed on state-selected NO fragments in order to further characterize the stereodynamics of this reaction. Preliminary measurements of relative Λ doublet propensities along with ab initio calculations confirm that both pathways arise from roaming-type mechanisms, but each pathway arises from roaming on a different electronic potential. This model assumes that NO3 dissociation takes place in the molecular plane which is supported by speed-dependent vector correlation measurements. This compelling evidence opens additional questions regarding this unusual reaction mechanism and the prevalence of multistate roaming in other molecular systems.

Tuesday, February 28, 2012
IQSE 578, 12:30 p.m.
Mitchell Physics Building

Institute for Quantum Science and Engineering
Texas A&M University

(Brown Bag Lunch)