REGULARITIES IN SPECTRA OF DOUBLY EXCITED-STATES OF 2-ELECTRON ATOMS

The classification of doubly excited intrashell states of two-electron atoms with a nucleus charge Z is studied. A relation is established between the quantum numbers in the Euler angle representation and the O(4) scheme of Herrick and Kellman (1980). Using the approximate solution to the Schrodinger equation, the interelectron repulsion (r12−1) is obtained as a function of the quantum numbers for the lower states of n-manifolds. This relation, together with the asymptotic one for the upper edge, is the basis of the formula which can be used to describe (r12−1) for all intrashell states. It is shown that the screening constant S for the lower states of all n-manifolds is a function of the universal parameter x, dependent on the quantum number; in the large-Z limit this function is fully determined by the formula for (r12−1). The linear section S(x) corresponds to a rovibrational spectrum structure of double excitations. A vibration frequency and a rotation constant are found analytically as functions of Z and principal quantum number n. The trends in the Q doubling derived by Herrick and Kellman are refined and supplemented. © 1990 IOP Publishing Ltd.