Close-coupling calculations of electron-atom scattering yield excitation cross sections for atomic eigenstates of relatively small principal quantum number $n\le n_{\max }$ and orbital angular momentum $l\le l_{\max }$ included in the close-coupling expansion. We use the photoionization of the helium system to demonstrate that finite convergent close-coupling calculations can be used to estimate the excitation cross sections of the residual ion to arbitrarily high principal quantum number $n>n_{\max }$ and orbital angular momentum $l>l_{\max }$. In doing so, we demonstrate the utility of the step-function property of the positive-energy state cross sections, together with the negative-energy state cross sections, in determining the desired cross sections for arbitrarily high Rydberg states.

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• Atomic & molecular collisions
• Electronic excitation & ionization