title: Intrashell electron-interaction-mediated photoformation of hollow atoms near threshold.
abstract: 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.
authors.affiliation: ESRF, 6 rue Jules Horowitz, B.P. 220, F-38043 Grenoble cedex, France.
authors.forename: S
authors.initials: S
authors.lastname: Huotari
authors.forename: K
authors.initials: K
authors.lastname: Hämäläinen
authors.forename: R
authors.initials: R
authors.lastname: Diamant
authors.forename: R
authors.initials: R
authors.lastname: Sharon
authors.forename: C C
authors.initials: CC
authors.lastname: Kao
authors.forename: M
authors.initials: M
authors.lastname: Deutsch