No Straight Path: Roaming in Both Ground- and Excited-State Photolytic Channels of NO 3 → NO + O 2

Abstract

Exclusive Roaming How do polyatomic molecules fall apart? The basic model, supported by centuries of chemical theory and experiment, invokes a series of internal rearrangements that lead to a fleeting high-energy transition-state geometry from which lower-energy products emerge. Over the past decade, several molecules have been shown to manifest a competing dissociation mechanism such that alongside trajectories that pass through the transition state, there are energetically accessible pathways that roam around it. Grubb et al. (p. 1075 ; see the Perspective by Jordan and Kable ) showed that the light-induced reaction of NO 3 to form NO and O 2 proceeded exclusively by roaming. Although there are distinct pathways to the products in two different electronic states, neither one passes through a conventional transition state.