The formation and ejection of endohedral Cs@C60+ by low energy collisions (35–220 eV) of Cs+ ions with surface adsorbed C60 molecules

Abstract

The collisional insertion of Cs+ ions into surface adsorbed C60 molecules was studied by scattering Cs+ ion beams from a C60 layer deposited on gold over the 35–220 eV impact energy range. Both Cs@C60+ and C60+ ions were ejected from the surface following the Cs+ impact but each species was characterized by different impact energy dependent yields and internal temperatures. Clear evidence for the endohedral nature of the complex is given. Both the scattering dynamics (at impact energies up to ∼100 eV) and the instant rise of the Cs@C60+ signal with the Cs+ beam onset clearly demonstrate that the insertion/ejection process is basically a single collision event. The outgoing Cs@C60+ and C60+ ions fragment during their flight time, after leaving the surface, via sequential emission of C2 units down to Cs@C50+ and C44+, respectively. Relative impact energy dependent yields were measured for both parent species and for all fragments. The yield curves are kinetically shifted with respect to each other as expected. Comparing the impact energy dependent fragmentation patterns of C60+ and Cs@C60+ we conclude that the ejected Cs@C60+ ion is much hotter than the C60+ ion. The internal vibrational excitation for both species is reaching a maximal value around 90–110 eV impact energy and than gradually decreases with increase in impact energy. The integrated Cs@C60+ yield is strongly peaked at around 80±5 eV impact energy. At impact energies above 120 eV also a C60− signal is observed but no Cs@C60− could be detected.