The $α$-dependence of transition frequencies for ions Si II, Cr II, Fe II, Ni II, and Zn II

Abstract

We performed accurate calculation of $α$-dependence ($α=e^2/hc$) of the transition frequencies for ions, which are used in a search for the variation of the fine structure constant $α$ in space-time. We use Dirac-Hartree-Fock method as a zero approximation and then the many-body perturbation theory and configuration interaction methods to improve the results. An important problem of level pseudocrossing (as functions of $α$) is considered. Near the crossing point the derivative of frequencies over $α$ varies strongly (including change of the sign). This makes it very sensitive to the position of the crossing point. We proposed a semiempirical solution of the problem which allows to obtain accurate results.

8 pages, revtex4 class, 2 eps figures