Vector correlations in dissociative charge transferinduced in He+-O2, N2 collisions at mediumenergies

Abstract

The dissociative ionization of O2 and N2 moleculesfollowing electron capture in He+-O2, N2 collisionshas been investigated in the keV energy range with a new devicewhich combines imaging and time-of-flight resolved coincidencetechniques. The (VHe+, VHe, VO+(N)+) velocity vector correlation consists of measuringthe VHe and VO+(N)+ velocities of theHe scattered neutral and O+ (N+) fragment ion producedby the same collision event, for a well defined VHe+ incoming projectile velocity. It leads to akinematically complete analysis of the collision. The subsequentkinetic energy correlation provides direct identification ofall the quasi-resonant, exoergic and endoergic processes interms of their reaction pathway, namely the intermediatemolecular ion excited state in the Franck-Condon regionand the corresponding dissociation limit. The spatial analysisof the velocity vector correlation for the dissociativeionization events enables us to investigate for each process thedependence of the electron capture probabilities upon thealignment of the molecular axis with respect to the VHe+ collision velocity and to the collision plane.Significant spatial anisotropies are observed for the endoergicprocess involving the excitation of the N2+ (F 2Σg+) state in He+-N2collisions at 1.5 and 3 keV, and visualized in the (χc, ϕc) angular correlation diagram, whereχc and ϕc are the polar and azimuthalangles which characterize the molecular axis orientation in thecollision frame.