The differential cross sections for chemi-ionization in Na + I Na+ + I- collisions are explained qualitatively , via the general shape of the deflection function , with a semi-classical atom-atom model for ion pair formation in molecular collisions .
In order to interpret the results quantitatively , the potential parameters and the classical deflection function of the system are determined by fitting the results calculated according to the model with the experimental results . Based on the potential parameters and the deflection function thus determined, the absolute values of the differential cross section of the collision are calculated and compared to the measurements . The comparison between the experimental and the theoretical cross sections in the fitting procedure is facilitated by the rainbow and the Stueckelberg structure.
Because of a serious disagreement between theory and experiment , a new quantitative interpretation is given, based on an extension of the model: not only the Landau-Zener coupling, but also the rotational coupling is taken into account .