Oxygen atom roaming and multiple dissociation pathways of NO$_{3}$

The role of nitrate radical (NO$_{3})$ photolysis in atmospheric has long been known, but mysteries remain regarding the mechanism of the dissociation. In particular, the NO + O$_{2}$ channel has proven to be a challenge both theoretically and experimentally. High resolution velocity map ion imaging studies reveal that there are two distinct mechanisms to form the NO + O$_{2}$ products. Additionally, the dominant of these mechanisms appears to be the non-traditional state ``roaming'' mechanism recently identified in formaldehyde dissociation. The roaming mechanism involves large amplitude motion associated with a frustrated radical dissociation before roaming oxygen atom abstraction to form O$_{2}$. The identification of roaming in the NO$_{3}$ reaction may imply the widespread importance of this type of mechanism in atmospheric chemistry.