355 nm Photodissociation of N₂O₃ Revealed by Velocity-Mapped Ion Imaging

Dinitrogen trioxide is proposed as a precursor to forming nitrous acid, an important source of hydroxyl radicals in the atmosphere. The spectroscopy and properties of N₂O₃ have been studied at high pressures or low temperatures, but there are no reports of its gas-phase photodissociation. This study investigates the 355 nm photodissociation of N₂O₃ in a DC-sliced velocity-mapped ion imaging apparatus using linearly polarized nanosecond pump and probe lasers. The N₂O₃ sample was generated by expanding NO and NO₂ seeded in a He carrier gas. After photodissociation, a high fraction of the available energy ends up in translation of the products. Time-dependent density functional theory calculations confirm the parallel transition dipole assignment if the dissociation occurs from a nonplanar N₂O₃ conformation. The vector correlations are nearly at the physical limits for a system where μ||v⊥J. The DC-sliced velocity-mapped ion imaging technique is well-suited to investigate N₂O₃ photodissociation since it resolves product speeds and differentiates among the sources of NO⁺ in an expansion containing NO, NO₂, HONO, and N₂O₃.