Sum rules for an atomic hyperfine structure in a magnetic field
The sum rules for the energy levels of a hyperfine multiplet in a constant uniform magnetic field are presented. It is found that for any value of the electron angular moment and the nuclear spin there are certain linear combinations of energy levels that do not depend on the magnetic field and can be used to determine the unperturbed hyperfine-structure separation in the presence of a perturbing magnetic field. It is also demonstrated that there are other linear combinations that are linear with the external magnetic field and hence can be used to determine bound values of the electron and nuclear magnetic moments. The accuracy of the approximation within which the result is valid is also discussed.PACS Nos.: 32.10.Fn, 32.60.+i1