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

The photodissociation of HONO2 at 193 nm has been investigated by phot ofragment translational spectroscopy. Two competing primary dissociati on processes were found: (1) HONO2-->OH + NO2 (60%) and (2) HONO2-->HO NO+O(1D) (40%). The translational energy distribution of reaction (1) shows two components which correspond to the formation of stable and u nstable (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 el ectronic transition dipole moment mu of the excitation which is orient ed parallel to the line connecting the two terminal O atoms in the par ent molecule.