Modified method of perturbed stationary states. I. Wave-theoretic formulation

The reaction-coordinate approach of Mittleman is used to generalize the method of perturbed stationary states. A reaction coordinate and an associated electron coordinate are defined for each state in the scattering expansion in terms of scalar parameters which depend on the internuclear separation. These are to be determined from a variational principle described by Demkov. The choice of parameters, the scattering expansion, and the Lagrangian for the radial scattering functions are given for a heteropolar one-electron system.