PHOTOIONIZATION BY PHOTOABSORPTION OF A TWO--ELECTRON ATOM OR ION
AND THE PROPERTIES OF THE TWO--ELECTRON WAVE FUNCTIONS

T. Suri\'{c}$^{*}$, R. H. Pratt$^{\dag}$ and E. G. Drukarev$^{\ddag}$

$^{*}$R. Bo\v{s}kovi\'{c} Institute, Zagreb, Croatia
$^{\dag}$University of Pittsburgh, Pittsburgh, PA, USA
$^{\ddag}$Petersburg Nuclear Physics Institute, St. Petersburg, Russia

We describe within a unified nonrelativistic approach single and double
photoionization of two electron atoms by photoabsorption at high photon
energies $\omega$ (but still $\omega \ll m$). The singularities of the
Coulombic interactions (e--e and e--N) determine the high energy behavior of
the processes and in the case of double ionization explain the shake--off and
quasi--free contributions at high energies, and in single ionization explain
deviations from IPA predictions.