Angular distribution of δ electrons emitted in collisions of 1.0-MeV/u Fq+ (q=4,6,8,9) with molecular hydrogen

The angular distribution, as well as the energy distribution of δ electrons produced in collisions of 1.0-MeV/u Fq+ (q=4,6,8,9) ions with molecular hydrogen, have been studied for laboratory observation angles (θL) from 0 degree to 70 degree with respect to the beam direction. The measurements are in fair agreement with the impulse approximation calculations which use the quantal elastic electron-ion differential scattering cross sections folded with the Compton profile of the target electrons. We observe that the energy of the centroid of the binary-encounter-electron (BEE) peak is projectile charge state, q, and laboratory angle, θL, dependent. Moreover, at 0 degree, an enhancement of the ratio of the observed double differential cross section for nonbare projectiles to that for the bare ion projectiles, σ(q+)/σ(9+), is observed, contrary to the q2 scaling predicted by a first Born calculation for ionization. This ratio σ(q+)/σ(9+) decreases nonotonically with increasing θL, and becomes smaller than one for θL≥30 degree