Probing the presence and absence of metal-fullerene electron transfer reactions in helium nanodroplets by deflection measurements

Abstract

Metal-fullerene compounds are characterized by significant electron transfer to the fullerene cage, giving rise to an electric dipole moment. We use the method of electrostatic beam deflection to verify whether such reactions take place within superfluid helium nanodroplets between an embedded C₆₀ molecule and either alkali (heliophobic) or rare-earth (heliophilic) atoms. The two cases lead to distinctly different outcomes: C₆₀Na_n (n = 1–4) display no discernable dipole moment, while C₆₀Yb is strongly polar. This suggests that the fullerene and small alkali clusters fail to form a charge-transfer bond in the helium matrix despite their strong van der Waals attraction. The C₆₀Yb dipole moment, on the other hand, is in agreement with the value expected for an ionic complex.