Using classical dynamics we analyze the ionization of the maximum angular-momentum circular Rydberg orbits of the hydrogen atom in strong circularly polarized microwave radiation. We find the ionization threshold generally higher than that for the static field, depending upon the direction of rotation, and in some cases completely different than the prediction based upon the above barrier escape. Below the ionization threshold the system returns to its initial state after interacting with the smooth microwave pulse.

• Received 2 April 1992

DOI:https://doi.org/10.1103/PhysRevA.47.R1612