Journal of Chemical Physics, Vol.111, No.21, 9634-9641, 1999
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 kinetic energy release distributions are structureless at all photon energies. The average anisotropy parameter, , ranges between 0.7 and 1.2. The absolute magnitude and photon energy dependence of both average kinetic energy release, < E-T'>, and are inconsistent with a previously assumed impulsive mechanism. Experiments are also conducted with N-4(+) produced with similar to 0.6 eV internal excitation. This results in a reduction of the observed kinetic energy release and anisotropy parameter, implying 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 valence-bond calculations of Langenberg [Langenberg , Chem. Phys. 221, 225 (1997)].