A new region characterized by Lévy diffusion exists in collective motion between the adiabaic and diabatic limits. Repeated chaotic scattering off of level crossings, whose repulsive or attractive nature changes dynamically, can result in localization of the collective motion for arbitrarily periods of time, and anomalous diffusion.

• Received 16 December 1993

DOI:https://doi.org/10.1103/PhysRevLett.72.1990