Intrashell electron-interaction-mediated photoformation of hollow atoms near threshold.
Double photoionization (DPI) of an atom by a single photon is a direct consequence of electron-electron interactions within the atom. We have measured the evolution of the K-shell DPI from threshold up in transition metals by high-resolution x-ray emission spectroscopy of the Kh alpha hypersatellites, photoexcited by monochromatized synchrotron radiation. The measured evolution of the single-to-double photoionization cross-section ratio with excitation energy was found to be universal. Theoretical fits suggest that near threshold DPI is predominantly a semiclassical knockout effect, rather than the purely quantum-mechanical shake-off observed at the infinite photon energy limit.
Huotari
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ESRF, 6 rue Jules Horowitz, B.P. 220, F-38043 Grenoble cedex, France.
Hämäläinen
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Diamant
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Sharon
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Kao
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Deutsch
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