Orderly structure in the positive-energy spectrum of a diamagnetic Rydberg atom

We have observed orderly structure in the spectrum of lithium in the range -1≤E≤+8 ${\mathrm{cm}}^{\mathrm{-}1}$, in magnetic fields of approximately 6 T. The structure resembles series of Rydberg levels converging on Landau levels. Interactions between levels are evident, but the underlying orderly structure raises hopes that a quantum solution to the problem may be feasible. The structure occurs in a regime where the classical motion is believed to be chaotic.