Quantum physics of He near the double ionization threshold-quantum chaos and Wannier threshold law

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The proposed research includes three topics.The first is to study the level statistics of He and other atoms in relation to the questions of quantum chaos. The second is the study of the photoabsorption spectra of He in the energy region lying between the N=10-25 thresholds of He+. Until now both the theoretical and experimental investigations for the photoabsorption of He have been limited to about the N=9 threshold of He+. This energy region will become accessible as more intense light sources such as those from free electron XUV and soft-X-ray lasers come on line in a few years. Questions such as whether the photoabsorption spectra will exhibit Erickson fluctuations in the quantum chaos regime will be investigated. The third topic concerns the absolute double photoabsorption cross sections of He for energies near the double electron escape threshold. Calculations will be undertaken from about a few meV above the threshold to test the Wannier threshold law. No full ab inito calculations as yet have been able to probe the energy region within about 1 eV above the threshold.