A simple classical atom-atom model qualitatively explains the relative differential cross sections of chemi-ionization processes M + X2 M+ + (X + X-). However, there is still no reliable quantitative explanation . A simple classical atom-atom model is not sufficient for the explanation of ion-pair formation in molecular collisions.}
It has already been found that the total cross sections of collisions between Li or Na atoms and I atoms can be described using the Landau-Zener transition probability. The question is whether the differential cross section of such a simpler system can also be explained using the Landau-Zener model.
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The differential cross section of the collision process have been determined in a later article and it was found that the cross section is indeed described by the simple atom-atom model with the Landau-Zener transition probability .
For a more detailed study the experimental resolution should be enhanced. Recently we have replaced the sputtering source by a charge-exchange source In the near future we shall determine the potential parameters of some alkali atom-halogen molecule potential curves by quantum-mechanical calculations and with the help of better resolved differential cross sections.