Oscillatory behavior of Rydberg-state total cross sections in the collisions Ne + -He and He + -Ne

The ${\mathrm{Ne}}^{+}$-He and ${\mathrm{He}}^{+}$-Ne collisions have been studied by means of optical spectrometry in the projectile energy range 10-150 keV. Very similar and regular oscillations in the Rydberg-state total cross sections are found for He I in both collisions and for singlet as well as triplet excitation. These oscillations are well described by the Rosenthal model. The Hei $4d^{1,3}D$ states display two superimposed oscillations for center-ofmass collision energies above 6.4 keV. We interpret this as the opening of a third exit channel, believed to be the He i $4f^{1,3}F$. No (or very little) structure is found in the Rydberg-state total cross sections for He ii, Ne i, Ne ii, or Ne iii levels.