Comment on ‘‘Circular Rydberg orbits in circularly polarized microwave radiation’’

Rzazewski and Piraux have investigated the ionization of circular Rydberg states in circularly polarized microwave fields [Phys. Rev. A 47, R1612 (1993)]. They find the threshold higher than for a static field and ‘‘in some cases completely different than the prediction based upon the above barrier escape.’’ We show that above barrier, stable orbits, may exist, which explains, in part, this finding by Rzazewski and Piraux.