A SEMICLASSICAL STUDY OF LONG-TIME RECURRENCES IN THE FEMTOSECOND PREDISSOCIATION DYNAMICS OF NAI

The existence of sharp (almost nonpredissociating) levels is shown to explain unexpected long time (30 ps) recurrences in the femtosecond dynamics of NaI. The semiclassical theory of predissociation line widths is used to show that the effect, which persists over a wide initial rotational state population, arises from a combination of the many coherently excited upper state levels, the long lifetimes of some of these levels, and a small vibrational anharmonicity that fixes the precise secondary recurrence time. Details vary from one assumed potential to another, but the broad conclusions are quite robust.