Wigner photoemission time delay from endohedral anions

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Characteristic features of Wigner photoemission time delay from endohedral anions A@${\mathrm{C}}_{60}{}^{q}$ along with their dependence on the anion charge $q$ are unraveled. Specifically, significant enhancement of the time delay in the innermost dipole photoionization channels near threshold is found, owing to the presence of the Coulomb confined resonances (CRs). Moreover, it is shown that interchannel coupling of the inner-shell Coulomb CRs with outer-shell photoionization channels results in resonantly enhanced time delay in the release of the outer-shell photoelectron well above, several hundreds eV, the outer-shell thresholds. It is also demonstrated that, and explained why, photoionization cross sections of the innermost subshells as well as outer subshells (near the inner-subshell threshold) depends only very weakly on the anion charge $q$, but the dependence of the corresponding time delays on $q$ can be significant. Furthermore, Coulomb CRs are found to emerge in the innermost quadrupole photoionization channels as well, thereby causing considerable time delay in the quadrupole photoemission. These findings are illustrated in calculations of the photoionization of inner and outer subshells of the endohedral anions Ne@${\text{C}}_{60}{}^{\ensuremath{-}1}$ and Ne@${\mathrm{C}}_{60}{}^{\ensuremath{-}5}$ that were chosen as case studies.