Electron-momentum distributions in singly ionizing C6+−He collisions at intermediate velocities

The process of single ionization has been studied in ${\mathrm{C}}^{6+}\ensuremath{-}\mathrm{He}$ collisions at the collision velocities of 1.17, 1.36, and 1.63 a.u. Ejected electrons were detected in coincidence with the recoil ions. Two components of the electron-momentum and the full-momentum vector of the recoil ion were measured. From these, two-dimensional momentum-space distributions of the continuum electrons were deduced, projected parallel or perpendicular to the collision plane, and for several values of the recoil transverse momentum. The distributions do not show the molecular-orbital-like patterns seen in similar collisions with singly and doubly charged projectiles. They do tend to lie preferentially along a ridge joining the target and projectile velocities, and show an increasing tendency to go in the direction of the projectile, both longitudinally and transversely, as the collision velocity is raised and the impact parameter lowered. The results are in agreement with classical trajectory Monte Carlo predictions for similar systems.