The interaction of $He^{-}$ with fullerenes

TL;DR

This study investigates how helium anions interact with fullerene clusters in helium nanodroplets, revealing a concerted double electron transfer mechanism and factors influencing dianion formation.

Contribution

It uncovers a novel double electron transfer process from He- to fullerene clusters and proposes a detailed mechanism involving long-range transfer and Coulomb explosion effects.

Findings

Double electron transfer from He- to fullerenes occurs concertedly.

Threshold size n ≥ 5 for dianion formation due to Coulomb explosion.

Adding water enables observation of smaller dianions.

Abstract

The effects of interactions between He- and clusters of fullerenes in helium nanodroplets are described. Electron transfer from $He^{-}$ to $(C_{60})_n$ and $(C_{70})_n$ clusters results in the formation of the corresponding fullerene cluster dianions. This unusual double electron transfer appears to be concerted and is most likely guided by electron correlation between the two very weakly bound outer electrons in $He^{-}$. We suggest a mechanism which involves long range electron transfer followed by the conversion of $He^{+}$ into $He_{2}^{+}$, where formation of the $He-He$ bond in $He_{2}^{+}$ releases sufficient kinetic energy for the cation and the dianion to escape their Coulombic attraction. By analogy with the corresponding dications, the observation of a threshold size of n \geq 5 for formation of both $(C_{60})_n^{2-}$ and $(C_{70})_n^{2-}$ is attributed to Coulomb explosion rather than an energetic constraint. We also find that smaller dianions can be observed if water is added as a co-dopant. Other aspects of $He^{-}$ chemistry that are explored include its role in the formation of multiply charged fullerene cluster cations and the sensitivity of cluster dianion formation on the incident electron energy.