Photodissociation dynamics of N-4(+) in the 300-670 nm range

The photodissociation of N-4(+) produced in a supersonic jet ion source is studied in an octopole ion guide at selected wavelengths in the 300-670 nm range. The N-2(+) photofragment recoil velocity distributions are measured using the guided-ion beam time-of-flight (GIB-TOF) technique. The derived k inetic energy release distributions are structureless at all photon energie s. The average anisotropy parameter, <beta >, ranges between 0.7 and 1.2. T he absolute magnitude and photon energy dependence of both average kinetic energy release, < E-T'>, and <beta(E-T')> are inconsistent with a previousl y assumed impulsive mechanism. Experiments are also conducted with N-4(+) p roduced with similar to 0.6 eV internal excitation. This results in a reduc tion of the observed kinetic energy release and anisotropy parameter, imply ing that different regions of the excited state surfaces are accessed when ion vibrational modes are excited. The observations can be rationalized by invoking excited states with bent equilibrium geometries, consistent with v alence-bond calculations of Langenberg [Langenberg , Chem. Phys. 221, 225 ( 1997)]. (C) 1999 American Institute of Physics. [S0021-9606(99)00645-5].