Inner-shell near-threshold photoionization of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>A</mml:mi><mml:mi>@</mml:mi><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">C</mml:mi></mml:mrow><mml:mrow><mml:mn>60</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>endohedral atoms
Annotatsiya
Photoelectron angular distributions and total photoionization cross sections of near-threshold $1s$ photoionization of Li from the oriented-in-space endohedral $\mathrm{Li}@{\mathrm{C}}_{60}$ fullerene are investigated within the framework of our recently developed photoionization theory of multicenter formations. Both at-the-center and off-the-center endohedral Li are considered, and off-the-center effects are shown to be of extreme importance, in contrast to the conventional wisdom. Multiple-scattering effects on the outgoing photoelectron are included and found to influence the photoionization spectra strongly, e.g., decreasing the cross section by more than an order of magnitude in certain cases, as compared to the situation when such effects are neglected. Diffraction resonances in the photoionization cross section of the endohedral Li atom are found as a result of the multicenter nature of the ${\mathrm{C}}_{60}$ surrounding cage, and these are compared with the results of other empirical and ab initio theories. Since there is nothing particularly special about Li $1s$ with respect to photoionization, the trends uncovered in this paper should qualitatively apply to near-threshold inner-shell $\mathrm{ns}$ photoionization spectra of virtually any endohedral atom A from any $A@{\mathrm{C}}_{60}$ endohedral fullerene formation.