Spectrum of the hydrogen atom and hydrogenlike ions in the magnetic field of a neutron star

The structure of hydrogenlike ions subject to an ultrastrong pulsar magnetic field is discussed. The finite-difference technique is applied in the context of perturbation theory to calculate the energy levels of the ground and several excited states of the hydrogen atom in fields of strength 2.35 x 109--4.7 x 1012 gauss. The energies of levels between which electric-dipole transitions should be most likely to occur are calculated for the hydrogenlike ions He II, C VI, N VII, O VIII, Ne X, Mg XII, Si XIV, S XVI, Ca XX, Fe XXVI. These transitions would produce Lα photons if a magnetic field were absent. X-ray pulsars with B = 1011--1013 gauss might have emission lines in the 0.1--21 keV energy range representing these transitions