Atomic resonances in parallel electric and magnetic fields

In a quantum mechanical treatment, an atom in external parallel electric and magnetic fields ionizes at energies above the classical ionization threshold and, at energies below tunnels through a potential barrier, in each case forming quasi-bound states (resonances). Such resonances can be calculated for hydrogen using the complex-coordinate method. The combination of this method with the R-matrix method allows the corresponding resonances to be calculated for non-hydrogenic Rydberg atoms. We employ such a combination of methods in an investigation of these resonances in sodium for various relative strengths of parallel, laboratory strength, external fields. Results are also presented for hydrogen in strong fields.