Crossing in odd alkaline-earth isotopes induced by hyperfine interaction

In an odd isotope with nuclear spin I not=O of an atom, the sublevels usually degenerate at certain points in energy ordinate which they call crossings. In alkaline-earth atoms, there is a series of crossings and it is determined only by the hyperfine splitting of the first ionisation limit ms 2 S 1 2/. A formula which is used to calculate the crossings has been derived. By using this formula, the framework of the sublevels and the experimental profile can be anticipated without knowing any detailed information about the odd isotope except for the hyperfine splitting of the first ionisation limit ms 2 S 1 2/.