Two-dimensional imaging of state-selected photofragments: the 355 nm photolysis of NO2

Two-dimensional photofragment imaging has been applied to the 355 nm photodissociation of NO2 in a supersonic beam. The NO fragments are state-selectively ionized and projected onto a two-dimensional position-sensitive detector. The original velocity distribution is reconstructed by an Abel transform of the observed image of the fragments. The speed distribution of a single rovibrational state of NO consists of a single peak as expected from conservation of momentum and energy. The anisotropy parameter, β, of the NO photofragments is found to be 1.40±0.20, which is significantly larger than previously reported values measured with effusive molecular beams. This discrepancy is explained by the effect of the rotation of the parent molecule.