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

TL;DR

This study investigates whether metal-fullerene electron transfer reactions occur within helium nanodroplets by measuring the resulting electric dipole moments, revealing that alkali metals do not transfer charge while ytterbium does, indicating different bonding mechanisms.

Contribution

The paper demonstrates the use of electrostatic beam deflection to probe charge transfer reactions in helium nanodroplets, distinguishing between ionic and non-ionic complexes.

Findings

C60Na_n shows no dipole moment, indicating no charge transfer.

C60Yb exhibits a strong dipole moment consistent with ionic bonding.

Charge transfer reactions depend on the metal atom type within helium droplets.

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 C$_{60}$ molecule and either alkali (heliophobic) or rare-earth (heliophilic) atoms. The two cases lead to distinctly different outcomes: C$_{60}$Na$_n$ ($n$=1-4) display no discernible dipole moment, while C$_{60}$Yb 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 C$_{60}$Yb dipole moment, on the other hand, is in agreement with the value expected for an ionic complex.