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Abstract=A08-m1d

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Relative differential cross sections have been measured for the atom-atom collision process $\Na+\I\to\Na^++\I^-$ at kinetic energies from 13 to 85 eV. The measurements show two types of oscillating features. The Stueckelberg oscillations are due to the interference of scattering from different potentials inside the pseudo-crossing of the covalent and ionic potential curves. Interference due to scattering from the ionic interatomic potential causes a rainbow structure that has been resolved completely . The measurements allow estimations of the covalent potential parameters and the pseudocrossing parameter H₁₂ . Semiclassical differential cross sections have been calculated using the lowest-order stationary-phase approximation, JWKB phase shifts and the Landau-Zener transition probability . When the known ionic potential and the determined covalent one are substituted, there is a very good agreement between the calculated and measured differential cross sections due to collisions with small and intermediate impact parameters . For large impact parameters a rather serious disagreement arises between the relative intensities as well as the oscillation wavelengths of the corresponding cross section . The intensity discrepancy has been removed taking into account the phenomenon of rotational coupling . .