Quasi-penning resonances of a Rydberg electron in crossed electric and magnetic fields

It is shown that the combination of crossed electric and magnetic fields and the Coulomb field of the atomic nucleus can lead to the localization of the Rydberg electron in the vicinity of the Stark saddle point. The localization principle is shown to be similar to the one which serves as the basis for a Penning trap. The localized electron is expected to give rise to quasibound states near and above the saddle-point ionization limit. These states are expected to cause modulations in the threshold photoionization cross sections.