Fast charged-particle impact ionization of endohedral atoms

The differential generalized oscillator strengths for ionization of the $s$ subshells of He and Ne atoms encapsulated inside a fullerene, ${\text{\cyrchar\CYRS{}}}_{60}$ cage, along with the single differential cross sections for ionization by fast electrons are calculated. The calculations have been performed using the two different model potentials to represent the fullerene shell. It is shown that the modulations of the wave function of the ejected electron caused by the interference between direct ejection and the waves scattered by the fullerene shell result in confinement resonances in the generalized oscillator strengths and the resulting impact-ionization cross sections. When the energy transfer to the target is close to that of the giant plasmon resonance in ${\text{C}}_{60}$, the interchannel interaction of the atomic ionization channels with the ${\text{C}}_{60}$ ionization channels significantly influences the cross section for impact ionization of the confined atom. The formulas describing this interaction are derived and it is shown that for small momentum transfer this interaction is related to the dynamic polarizability of ${\text{C}}_{60}$. The general formulas are used to calculate impact ionization both of the He atom confined in ${\text{C}}_{60}$ and of the empty ${\text{C}}_{60}$ cage. The cross section of the latter process is compared to available experimental data.

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