On different mechanisms of the two-electron atomic photoionization

We evaluate the partial contribution of different mechanisms leading to the single-photon two-electron atomic ionization processes: photoionization with excitation and double photoionization. We estimate the photon energy at which the shake-off mechanism becomes dominant over the two-step mechanism. We support our findings by scaling the photoionization cross sections of neutral atomic species with the electron scattering cross sections on the corresponding positive ions.