Suppression of ionization stabilization in a driven Morse-Soft-Coulomb system

Abstract: Ionization stabilization is a well-known phenomenon in strongly driven Soft-Coulomb atomic models, where the ionization probability decrease as the field amplitude increases. In this work, we investigate how this mechanism is affected by introducing a repulsive Morse barrier into the binding potential, leading to a Morse-Soft-Coulomb (MsC) model. A systematic comparison between the Soft-Coulomb and Morse-Soft-Coulomb systems is performed for different values of the softening parameter. Ionization probabilities, escape-time maps computed on the field-free energy shell and representative trajectories reveal that the stabilization window observed in the Soft-Coulomb model is strongly suppressed in the Morse-Soft-Coulomb system. To elucidate the origin of this behavior, we analyze the corresponding Kramers-Henneberger effective potentials. While the Soft-Coulomb model develops a symmetric double-well structure supporting two equivalent trapping regions, the Morse-Soft-Coulomb potential exhibits a single effective minimum as a consequence of the broken left-right symmetry introduced by the Morse branch. The combined analysis of ionization probabilities, escape dynamics, representative trajectories, and Kramers-Henneberger potentials indicates that the suppression of stabilization is closely associated with the modification of the phase-space transport structures and the reduction of the effective trapping region induced by the Morse