Breakdown of asymptotics of the double photoionization of helium at the high-energy limit

It is shown that the contribution to the double-to-single ionization ratio ${\mathrm{\sigma }}^{2+}$(ω)/${\mathrm{\sigma }}^{+}$(ω) of helium caused by small momentum transfer breaks down the asymptotics of this ratio at the high-energy limit. The addition of up to 10% at ω=12 keV is expected to cause a slope in the ratio, which can be related to the properties of the ground state. The contribution is expected to be important also in the analysis of the double photoionization of ${\mathrm{H}}^{\mathrm{-}}$ and ${\mathrm{H}}_2$.