Effect of the projectile charge on the ionization and excitation of hydrogen molecules by fast ion impact

The ratio of double ionization to single ionization (DI to SI) as well as the ratio of ionization excitation to single ionization (IE to SI) in hydrogen molecules were studied by examining the effect of the projectile charge q on these processes. The DI to SI and IE to SI ratios were measured at a fixed velocity (corresponding to 1 MeV/amu) from $q=1\mathrm{}$ to 20. For a highly charged ${\mathrm{Cu}}^{20+}$ projectile, for example, the DI to SI and IE to SI ratios are 13% and 46%, respectively, which is a large increase from the ratios of 0.18% and 1.95%, respectively, for ${\mathrm{H}}^{+}$ projectiles. The DI to SI ratio initially increases much more rapidly with projectile charge than the IE to SI ratio. The measured rate of increase of both these ratios decreases for highly charged projectiles. These trends are in agreement with a simple model calculation based on the independent electron approximation.