Asymptotic approximations to the energy of dispersion interaction between rubidium atoms in Rydberg states

Abstract

Irreducible components determining the dependence of the van der Waals coefficient C6 (nlJM) on the angle θ between the interatomic and the quantisation axes of two Rb atoms in their identical Rydberg states ∣nlJM> are evaluated with account of the most contributing terms of the spectral resolution for the bi-atomic Green’s function. Asymptotic polynomials in powers of the Rydberg-state principal quantum number n are derived for the C6 irreducible components. Numerical values of the polynomial coefficients are determined for Rb atoms in their n2S1 2, n2 P1 2,3 2, n2 D3 2,5 2 and n2F5 2,7 2 Rydberg states of arbitrary high n. The transformation of the van-der-Waals interaction law-C6 R6 into the dipole–dipole law C3 R3 in the case of close two-atomic states (the Förster resonance) is considered. Numerical values, the dependences on the magnetic quantum numbers M and on the angle θ of the constant C3 are determined together with the ranges of interatomic distances R, where the interaction law R-6 transforms into the law of R-3.