title: Roaming-mediated isomerization in the photodissociation of nitrobenzene.
abstract: Roaming reactions comprise a new class of reaction in which a molecule undergoes frustrated dissociation to radicals, followed by an intramolecular abstraction reaction. Nitro compounds have long been known to dissociate to give NO as a major product. However, rates based upon isomerization via calculated tight transition states are implausibly slow, so the key dissociation pathway for this important class of molecules remains obscure. Here, we present an imaging study of the photodissociation of nitrobenzene with state-specific detection of the resulting NO products. We observe a bimodal translational energy distribution in which the slow products are formed with low NO rotational excitation, and the fast component is associated with high rotational excitation. High-level ab initio calculations identified a 'roaming-type' saddle point on the ground state. Branching ratio calculations then show that thermal dissociation of nitrobenzene is dominated by 'roaming-mediated isomerization' to phenyl nitrite, which subsequently decomposes to give C(6)H(5)O + NO.
authors: Department of Chemistry, Wayne State University, Detroit, Michigan                 48202, USA.
authors: Michael L
authors: ML
authors: Hause
authors: Nuradhika
authors: N
authors: Herath
authors: Rongshun
authors: R
authors: Zhu
authors: M C
authors: MC
authors: Lin
authors: Arthur G
authors: AG
authors: Suits
mesh_terms: D007536:Isomerism; D009569:Nitric Oxide / Q000737:chemistry; D009578:Nitrobenzenes / Q000737:chemistry*; D010777:Photochemistry
chemical_list: D009578:Nitrobenzenes; D009569:Nitric Oxide; C036077:nitrobenzene