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A semiclassical over-barrier model for charge exchange between highly charged ions and one-optical-electron atoms

Absolute total cross sections for electron capture between slow, highly charged ions and alkali targets have been recently measured. It is found that these cross sections follow a scaling law with the projectile charge which is different from the one previously proposed which is based on a classical over-barrier model (OBM) and verified using rare gases and molecules as targets. In this paper we develop a `semiclassical' (i.e. including some quantal features) OBM in an attempt to recover experimental results. The method is then applied to ion-hydrogen collisions and compared with the result of a sophisticated quantum mechanical calculation. In both cases the present method is found to underestimate the correct result by a factor of two, but, where comparison can be made, it is superior to other OBMs. A qualitative explanation for the discrepancies is also given.