Alternative choices of Coulomb channel functions

A class of Coulomb radial functions is defined for use in atomic or molecular Rydberg multichannel quantum-defect calculations. The associated accumulated radial phase parameters beta(epsilon) have a simple functional dependence on the energy, analogous to the familiar Rydberg relation where beta(epsilon)=pi(n(*)-l), with n(*)=(-epsilon)(-1/2), enabling easy use in the empirical fitting of complex multichannel spectra. However, "false roots" at low-energy and strong energy dependences of the quantum defects are largely avoided in the approach, which also may be implemented in the framework of ab initio R-matrix calculations in a straightforward manner. The method is illustrated with one-channel and multichannel examples relating to atomic potassium, nitric oxide, and molecular hydrogen.