Shape variation of the two-electron photoionization spectrum with photon energy growth

We trace the evolution of the energy spectrum of both outgoing electrons emitted after absorption of a single photon with the latter's energy growth. We use quite precise non-variation two-electron initial state wave functions, obtained by Correlation Function Hyperspherical Harmonic Method. We obtain the values of $\omega_{1}$ and $\omega _{2}$ at which the spectrum curve changes it shape. At $\omega =\omega _{1}$ the usually considered $\mathbf{U}$-shape changes to $\mathbf{W}$-shape. At $\omega =\omega _{2}$ the central $\mathbf{W}$ peak splits into two. We consider ground states of the helium atom and of helium-like ions with the nuclear charge $Z$, the negative ion of hydrogen H$^{-}$ and the excited $n^{1}S$ state of helium. The limiting laws for $Z\gg 1$ and $n\gg 1$ are obtained. The analysis is carried out without calculations of the particular energy distributions. We believe that the predicted features could be observed experimentally detecting both outgoing electrons in coincidence.