CENTER-OF-MASS CORRECTIONS ON ATOMIC BINDING-ENERGIES IN A MAGNETIC-FIELD

Centre-of-mass corrections on the total energies of general atomic systems are investigated in the presence of a homogeneous magnetic field. Threshold energies can easily be defined from the ground-state energy of the subsystem. The general form of binding energies with respect to single-electron ionisation is then established as a function of binding energies obtained in an approximation where the nucleus mass is considered as infinite. A transverse collective motion of the atomic system is shown to reduce the binding energies, especially in the case of negative ions. Expressions for ionisation energies of one-electron and two-electron atoms are derived as examples. A detailed quantitative study of the H- and He atoms in very strong magnetic fields is presented. The H- binding energies are very sensitive to centre-of-mass effects. In particular, the H- bound spectrum becomes finite, in opposition to its properties in the infinite-protons-mass approximation.