Stabilization of electrons onArq+ions after slow collisions withC60

Abstract

We discuss hollow atom formation and stabilization of electrons on ${\mathrm{Ar}}^{q+}$ following ${\mathrm{Ar}}^{q+}+{\mathrm{C}}_{60}\ensuremath{\rightarrow}{\mathrm{Ar}}^{(q\ensuremath{-}s)+}+\ensuremath{\cdot}\ensuremath{\cdot}\ensuremath{\cdot}$ collisions at $3.3q \mathrm{keV}$ $(q=4--18).$ The experimental information consists of the final projectile charge-state distributions ${f}_{q}^{s},$ i.e., the relative distributions of the number of stabilized electrons, s, and the corresponding mean values $〈s〉={\ensuremath{\sum}}_{s=1}^{q}{\mathrm{sf}}_{q}^{s}$ as functions of q. We use the classical over-the-barrier model to deduce sequences of effective principal quantum numbers and find that the hollow atom formation is completed $3--{4a}_{0}$ above the surface of the ${\mathrm{C}}_{60}$ cage for all q. For $q<~8$ (filled L shells), the last electrons are transferred from delocalized outer ${\mathrm{C}}_{60}$ orbitals directly to the projectile M shell (side-feeding), while several intermediate shells are left open for larger q leading to further electron transfer at intermediate distances and simultaneous electron emission from higher projectile shells. At still closer distances, localized carbon K-shell electrons are transferred directly to the argon L $(q=10$ and 11) and M shells $(q>~12).$ The direct transfer to the L shell of ${\mathrm{Ar}}^{10+}$ and ${\mathrm{Ar}}^{11+}$ is manifested as significant enhancements of $〈s〉$ for $q=10$ and $q=11.$