title: Stereodynamics of multistate roaming.
abstract: We present a molecular level description of NO3→ NO + O2 photodissociation for both of the experimentally observed reaction pathways using the results of ion imaging experiments and recent theoretical studies. 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. Previous measurements (Grubb et al., Science, 2012, 1075-1078) of relative Λ doublet propensities along with ab initio calculations revealed that both pathways arise from roaming-type mechanisms, but each pathway arises from roaming on a different electronic potential. This model, however, assumes that NO3 dissociation takes place in the molecular plane. In the present paper, we have confirmed this assumption through speed-dependent vector correlation measurements. Strong perpendicular correlations between the velocity vector v and the angular momentum vector j are observed in the NO fragment originating from both pathways, in agreement with a constrained planar dissociation. These results are discussed in light of the absence of vector correlations in other roaming systems, which have previously been characterized by an unconstrained intra-molecular abstraction. We show that geometrical constraints should in fact be quite prevalent in roaming dynamics, and are analogous to the geometrical constraints of the corresponding bimolecular abstraction reaction.
authors.affiliation: Department of Chemistry, Texas A&M University, College Station, P.O. Box 30012, Texas 77842. swnorth@tamu.edu.
authors.forename: Michael P
authors.initials: MP
authors.lastname: Grubb
authors.forename: Michelle L
authors.initials: ML
authors.lastname: Warter
authors.forename: Simon W
authors.initials: SW
authors.lastname: North