PHOTODISSOCIATION OF NITRIC-ACID IN A COLD MOLECULAR-BEAM AT 193 NM

The photodissociation of HONO2 at 193 nm has been investigated by photofragment translational spectroscopy. Two competing primary dissociation processes were found: (1) HONO2-->OH + NO2 (60%) and (2) HONO2-->HONO+O(1D) (40%). The translational energy distribution of reaction (1) shows two components which correspond to the formation of stable and unstable (hot) NO2 photofragments with a ratio of 1:2. The decay of hot NO2 produces the secondary fragments NO+O(3P). The recoil anisotropy parameters associated with the respective dissociation processes beta(1) = -0.6 +/- 0.1 and beta(2) = +0.6 +/- 0.2 are consistent with an electronic transition dipole moment mu of the excitation which is oriented parallel to the line connecting the two terminal O atoms in the parent molecule.