Collision cross sections derived from a longhyphen;range potential can be made more realistic through the addition of a shorthyphen;range component. It is shown how this can be achieved with no loss of simplicity, and in agreement with experiment. Upon addition of a Coulombic term, improved expressions for ionndash;electron neutralization and thermionic emission are then obtained. These developments permit the transition between the small and large molecule regimes to be followed explicitly.
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