Coulomb Green-function approach to adiabatic Rydberg energy levels: Generalization to multichannel cases

This study concerns the determination of adiabatic electronic terms of $A^{\mathrm{*}}$-B systems where A is an atom whose spectral parameters are known from multichannel quantum-defect theory (MQDT) and B is a light rare-gas atom (He,Ne) in its ground state. The adiabatic terms are obtained as the roots of a transcendental equation for which the only required inputs are the MQDT parameters of A, the $e^{\mathrm{-}}$-B scattering s-wave phase shifts, and of course the internuclear distance R between the two atoms. The MQDT parameters of A are its eigenquantum defects and the unitary matrices relating the fragmentation channels to the short-range eigenchannels. It is found that for R (a.u.)≲2ν, ν being the effective principal quantum number relative to the highest ionization threshold involved in the MQDT analysis of A, the adiabatic spectra can be described by R-dependent Lu-Fano diagrams. The accuracy of this approximation increases as ν increases. Finally, some numerical results relative to the ${\mathrm{Ar}}^{\mathrm{*}}$-He system are presented and commented on.