Enhancement of intense field ionization of Rydberg atoms by nonhydrogenic cores and quantum-mechanical tunnelling

Time-dependent probabilities for ionization of Rydberg H, He, Li, Na and K in intense fields are calculated using a classical-trajectory method with allowance for quantum-mechanical tunnelling. The results depend only weakly on the nuclear charge and screening as long as the core is nonhydrogetlic. However, the differences from the hydrogenic target are dramatic. The core of the nonhydrogenic atoms is treated as a Is orbital in the case of He and as a Thomas-Fermi potential for the higher-Z atoms.