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 mu parallel to nu perpendicular to 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.