Quasi-molecular model in heavy particle collisions

In atom--atom collisions, heavy incident particles can strongly perturb the electronic edifice and are therefore not a probe as clean as are photons and electrons, to study electron correlations in an isolated system (atom, ion, molecule). On the other hand, after the hurricane caused by such violent collisions, the electronic clouds are left in very exotic states which are not commonly encountered with lighter perturbers; multiple excited and/or ionized states will occur. Furthermore, when the electronic clouds strongly interpenetrate the excitation process itself involve the interaction of several electrons of each partner. It is therefore no need to stress the importance of electron correlation in such processes