Coordinate asymptotic behavior of the wave function of two electrons in a Coulomb field

Asymptotics of the Coulomb two-electron wave function belonging to the continuous spectrum is studied, with the electron interaction taken into account. An explicit form for the zeroth coefficient in the expansion of the wave function in the asymptotical series over the powers of the parameter $R$ $(R=\sqrt{r_1^2+r_2^2})$ is found. Physical interpretation of the expression obtained is given. It is pointed out that the small value of the cross-section of the double photoionisation of Helium atom can be explained by the presence of the node surface in the final state wave function.