A study of low-energy differential ion-atom scattering. III. Na+-Na

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Abstract
For pt.II see ibid., vol.15, p.3695-707 (1982). Differential cross sections for Na+-Na scattering into the elastic and the 3p excited channel have been measured at centre of mass energies between 25 and 57 eV. The results are compared with a three-state calculation based on theoretical potentials and a 1 Sigma u-1 Pi u non-adiabatic coupling matrix element chosen by analogy to theoretical data for other alkali diatomic ions. The elastic cross sections exhibit an oscillation arising from Sigma g- Sigma u interference which makes them rather sensitive to the potentials. Whereas calculated and measured data, notably the phase of the oscillation, agree quite well in the angular range where only two states contribute, strong deviations are found where the 1 Pi u state participates, and also in inelastic scattering. It is shown that these deviations essentially are not due to errors in the Sigma u- Pi u coupling but that rather the potentials have to be corrected.