Radiative and thermal widths of Landau-excited hydrogen atoms in very strong magnetic fields

It is proved that in magnetic fields B>or approximately=10 7 T, which are characteristic of neutron stars, the lifetime of an electron in an excited Landau level (N>or=1) bound to a proton becomes identical to that of an electron moving freely along the magnetic field lines, viz. the lifetime with respect to cyclotron transitions. The associated widths are found to be larger than or at least comparable with the Coulomb binding energies (depending on the magnetic field strength) whence the nature of these states as discrete states is obliterated. The authors show that the anomalous magnetic moment of the electron and the finite mass of the proton cause additional level shifts comparable in magnitude with the Coulomb energies. Furthermore, they investigate thermal line broadening and find that, as a consequence of the pronounced anisotropy of the effective masses for motion parallel and perpendicular to the field, thermal broadening is strongly reduced for emission perpendicular to the field.