The dependence of H2+ molecular-ion yields on the proton neutral fraction

We have measured the fraction of H 2 + molecules emerging from 1.8−72 μg/cm 2 carbon targets bombarded with 0.75–2.25 MeV H 2 + and H 3 + projectiles. The H 2 + molecular yields decrease from ∼10 −3 for 1.8 μg/cm 2 to ∼10 −10 for 72 μg/cm 2 targets and are only weakly dependent upon the projectile velocity. The distance between the two protons upon emergence from the target depends upon the mutual Coulomb repulsion during the dwell-time in the target, upon multiple scattering, and upon the wake-potential. The velocity dependence of the molecular ion yield, for a given dwell-time, follows the proton neutral fraction. The dependence of the probability of H 2 + molecular-ion formation upon the proton neutral fraction, the projectile dwell-time, and the influence of multiple scattering are considered. Additional factors influencing the molecular ion yields were investigated in double-target experiments.