In a recent paper (Vrakking, M. J. J.; Lee, Y. T.; J. Chem. Phys. 1995, 102, 8833) we reported that autoionization rates of Xe Rydberg states converging on the 2P1/2 upper spin orbit state of Xe+ strongly depend on the presence of dc electric fields and surrounding ions. In the current paper, we present theoretical calculations that illustrate that the observed electric field dependence of the autoionization rates is influenced by the existence of short-range Rydberg electron-core interactions. In the presence of dc electric fields the autoionization rates decrease as a result of orbital angular momentum mixing. In the case of the ns'[1/2]1 series, mixing with the high-l manifold is mediated by short-range interactions with the rapidly autoionizing nd'[3/2]1 series. As a result, effective l-mixing takes place at substantially lower electric field strengths than would otherwise be the case. The experimental results of the dc electric field dependence of Xe pulsed field ionization (PFI) signals are compared with the theory, and predictions are made for sub-nanosecond time-resolved ionization experiments.