Anomalous autoionization lifetimes of Rydberg states in a circularly polarized microwave field

Recent experiments by Jones, Fu, and Gallagher [J. Chem. Phys. 106, 3578 (1997)] designed to mimic collisional effects on the lifetimes of ZEKE Rydberg states find that, in a circularly polarized microwave field, autoionization lifetimes of atomic Rydberg states exceed those in a linearly polarized field. Surprisingly, however, the lifetimes not only do nor display the expected n(5) scaling but are essentially independent of n for most of the states prepared in the experiment. Similar observations were made by Vrakking and Lee [J. Chem. Phys. 102, 8818 (1995)] in studies of NO Rydberg states. We present a classical model that predicts n-independent behavior of autoionization lifetimes over essentially the same range of It-values as in the experiments of Jones, Fu, and Gallagher. The origin of this behavior is traced to the particular combinations of field strengths and frequency used in the experiment. (C) 1998 American Institute of Physics.