Simultaneous ionization and excitation by photon absorption in He

Abstract

Second order terms of the time dependent perturbation theory expansion were used to calculate the simultaneous ionization and excitation of helium as result of a photon absorption. In this calculation, the perturbing Hamiltonian was assumed to be the sum of the interaction between the electrons and their interactions with the free radiation field. According to this model, the correlated transition resulting from the photon absorption can be calculated using the independent particle model to describe the atom states. In the present, the cross section for the correlated photon ionization in He was calculated using screened hydrogenic wave functions. The sum over the intermediate states required by the present approach was taken up to the tenth shell. No significant differences were observed in the results considering higher shells intermediate states. Correlated photon ionization cross section values are presented for energies of the absorbed photon varying from 70 up to 1500 eV and for transitions where the ionization of the helium atom is followed by simultaneous excitation of the second electron to a higher shell, that is He(1s 2)+ hν→He + (n s 1 or n p 1)+ e − , with n varying from 2 up to 6. Comparison of the present calculations with the results of measurements from several authors shows a very good agreement while the results of other theoretical calculations exhibit considerable discrepancies.