  In excited molecules, the interaction between the covalent Rydberg and
ion-pair channels forms a unique class of excited Rydberg states, in which the
infinite manifold of vibrational levels are the equivalent of atomic Rydberg
states with a heavy electron mass. Production of the ion pair states usually
requires excitation through one or several interacting Rydberg states; these
interacting channels are pathways for loss of flux, diminishing the rate of ion
pair production. Here, we develop an analytical, asymptotic charge transfer
model for the interaction between ultracold Rydberg molecular states, and
employ this method to demonstrate the utility of off-resonant field control
over the ion pair formation, with near unity efficiency.
