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

We trace the evolution of the shape of the two-electron photoionization spectrum with photon energy growth using quite a precise two-electron wave function, obtained by the correlation function hyperspherical harmonic method. We obtain the values of ω ₁ and ω ₂ at which the spectrum curve changes its shape. At ω=ω ₁ the U shape changes to a W shape. At ω=ω ₂ the central W peak splits into two. We consider ground states of the helium atom and of heliumlike ions with the nuclear charge Z, the negative ion of hydrogen H ^-, and the excited n ¹S state of helium. The limiting laws for n≫ 1 and n≫ 1 are obtained. The analysis is carried out without calculations of the particular energy distributions themselves.