NONHYDROGENIC RYDBERG STATES IN EXTERNAL FIELDS AS INTERMEDIATE RESONANCES IN MULTIPHOTON IONIZATION

We report wavelength spectra of multiphoton ionization of rubidium, in which the intermediate state is a Rydberg state (35<n<45). The photoelectron yield is measured for a free atom, for an atom placed in an external electric field, and for an atom in a magnetic field. Both the magnetic- and the electric-field spectra show a dramatic decrease in yield above n40. Our analysis centers on the field-induced mixing of states. The threshold occurs when the resonant state, which has a large quantum defect, mixes with the manifold. The analysis is also applied to experiments reported previously. © 1990 The American Physical Society.