Collisional processes of rubidium in the S and D Rydberg states with helium

The cross sections for quasi-elastic and inelastic collisional processes between rubidium in non-hydrogenic Rydberg nS and nD states and helium have been measured. The quenching cross section of the Rydberg levels seems to behave similarly for different series, it first increases with n and then reaches a maximum, which is more or less shifted towards low n values, depending on the proximity of the highly degenerate hydrogenic neighbouring levels. The authors' experimental results and those previously obtained are in fair agreement (within a factor of 3 in the worst cases) with the values computed using a simple theoretical approach only taking into account the Rydberg electron-helium interaction.