Abstract
A quantitative analysis of two sets of excited states of hydrogen atom in an arbitrary constant magnetic field is carried out for the first time. A 'nonlinearisation' method was used. Perturbational terms up to H6 are calculated. It is shown that the domain of applicability of the perturbation theory is contracted sharply with increase in the atom excitation degree. The range of this domain is estimated. Functional structure of arbitrary correction to the wavefunction is investigated and some of its substructures are found explicitly. Detailed calculations are performed for magnetic fields of arbitrary strengths. The accuracy of the calculations is estimated. Crossovers of the levels in the region of fields >or approximately=108 G are discussed. Possible experimental consequences are considered.