Classical impact parameter approximation: Application to atomic collisionswith n independent electrons and to recoil analysis

We show that a classical Impact Parameter Method may be derived when taking fully into account the smallness of the ratio between the electron and nuc lear masses. It allows to calculate; exactly as in the quantum version, pro jectile scattering and therefore recoil momenta required for the interpreta tion of recent measurements. We prove an additivity theorem which allows, i n particular, to reduce the n-non-interacting electron problem to a set of n one-electron problems. Consequences for the interpretation of target reco il measurements are discussed.