Photoionization spectra in parallel electric and magnetic fields

We present a quantum-mechanical method to evaluate photoionization spectra of atoms in parallel applied electric and magnetic fields, valid for a wide range of energies and field strengths. We identify different symmetry regions in configuration space and use R-matrix propagation, a frame transformation and a two-dimensional matching procedure to asymptotically defined solutions to solve the Schrodinger equation over all space. We use quantum defect theory to take into account nonhydrogenic atomic cores. We illustrate the method for the hydrogen atom in laboratory strength fields and for strong fields. We analyze the main features of the photoionization spectra for electric and magnetic-field strengths of 51.4 kV cm(-1) and 470 T, respectively. We identify three types of resonances, defined by their behavior upon varying the external fields and we explain this behavior in terms of the associated wave functions