Laser-induced fluorescence measurement of nascent vibrational and rotational product state distributions in the charge transfer of Ar++N2→Ar+N+2 (v=0,1) at 0.2 eV

Abstract

A novel experimental technique couples a flowing afterglow ion source with a supersonic nozzle expansion in order to deliver high densities of relatively low kinetic energy ions into a low pressure chamber. The technique is used to study the charge transfer reaction Ar+(2P3/2)+N2(v=0) →Ar(1S0)+N+2 (v+0,1;N)+ΔE=0.18 eV under single collision conditions at 0.24 eV c.m. Nascent rotational and vibrational state distributions are obtained by the method of saturated laser-induced fluorescence probing. It is found that a substantial fraction of the available energy is partitioned into internal excitation of the N+2 product molecule. The higher of the two energetically accessible vibrational levels N+2 (v=1) is populated in 89±9% of the charge transfer collisions. The nascent rotational distribution in N+2 (v=1) is characterized by a Boltzmann distribution with Trot=700±50 K. The results are compared with a number of recent state-selected experiments on charge exchange in ArN+2 , ArH+2 , and NCO+ systems. It is suggested the experimental findings are best explained in terms of the detailed locations of potential surface crossing seams, rather than by the widely used energy resonance or diatomic molecule, Franck–Condon ionization models.