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

The fraction of H2+ molecules emerging from 1.8-72μg/cm2 carbon targets bombarded with 0.75-2.25 MeV H2+ and H3+ projectiles has been measured. The H2+ molecular yields decrease from approximately 10-3 for 1.8μg/cm2 to approximately 10-10 for 72μg/cm2 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 H2+ 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. (Auth.)