Charge Exchange in Collisions Between Multiply Charged Ions and Neutral Hydrogen

The results of recent experimental studies of charge transfer by multiply charged ions in H and H 2 are considered in relation to current theoretical descriptions. At low velocities ( V < 1 a.u.) where the collisions are quasimolecular, curve-crossings can lead to large cross-sections. For high initial charge states q , cross-sections depend on q rather than ion species. No clear relationship between cross-sections in H and those in H 2 exists. At high velocities ( V > 1 a.u.) cross-sections in H and H 2 fall as V increases and scale according to q n where n is between 2 and 3 for many reactions. For completely stripped ions of atomic number Z , measured cross-sections appear to scale according to Z 3 at high velocities.