Dispersion coefficients for atoms in different states

Abstract

A formalism allowing the calculation of dispersion coefficients between atoms in different excited states is presented. The validity of the integral transformation involving dynamical polarizabilities of each atom at imaginary frequencies is discussed and for this case a partition of the second order energy which allows a partial separation into single centre contributions is proposed. With respect to the interaction of ground state atoms a new contribution, the dynamic induction due to the allowed downward transitions, appears. The C ₆ coefficients of H_1s + H_2s , H_1s + H_2p and H_2s + H_2s are calculated exactly. Approximate formulae are proposed and discussed. Upper and lower bounds are calculated by the method of Padé approximant for the interaction of excited hydrogen with ground state rare gas atoms.