Intensity distribution in the spectrum of highly excited atomic hydrogen in parallel electric and magnetic fields

The spectrum of highly excited atomic hydrogen subjected to axially symmetrical perturbations is considered. In particular, a study is made of the mixed Stark-Zeeman effect in parallel electric and magnetic fields. In the l-mixing regime general analytical expressions are obtained for the probability amplitudes and the oscillator strengths of transition to the low-lying levels. In the case of the atom in parallel electric and magnetic fields it is shown that a peculiar dependence exists of the electronic density at the nucleus on the relative strength of the two fields.