Abstract
Total photoionization cross sections of doubly excited He have been measured up to the single ionization threshold ${I}_{15}$ of ${\mathrm{He}}^{+}$ and calculated up to ${I}_{17}$ revealing excellent agreement. The fact that all spectra are dominated by principal Rydberg series is explained by the observation that the quantity $F=N\ensuremath{-}K$, representing angular motion, is an approximate quantum number for a large fraction of states. While the nearest-neighbor energy spacings between resonances of Rydberg series with small $F$ approach a Wigner distribution, reflecting chaos in radial motion, there is no indication for a transition to full chaos including angular motion.
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