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Researchers Create Fullerene Dianions in Liquid Helium

Researchers from the University of Innsbruck and the University of Leicester have collaborated to develop a new method of forming charged molecules.

They found that helium atoms could acquire excess negative charge, and this could make them become aggressive chemical reagents.

Helium is an unreactive gas. However, the gas becomes a superfluid when it is cooled to a temperature just above absolute zero. This superfluid helium has zero viscosity and demonstrates stronger-than-gravity capillary action.

The research team applied high pressure and low temperature to helium gas, which they then forced it go through a 5µm diameter pinhole into a vacuum chamber, where they became droplets. The researchers made these droplets to go through cells that had C60 or C70 fullerenes, and then used an electron beam with energy range between 0 and 150eV to hit the mixture.

When a 22eV was used, clusters that had more than four fullerene molecules acquired double negative charge, becoming stable dianions. Usually, when dianions are outside of chemical solutions they have a short life and are very unstable. This new method enables creation of fullerene dianions in liquid helium that are comparatively stable.

In this process, two electrons have simultaneously attached themselves to a fullerene molecule to form dianions. According to Coulomb's Law, it would be difficult to attach two electrons sequentially, as the electrons would repel each other.

However, helium has two negatively charged electrons, which are balanced by two positively charged protons. In this reaction, the electron beam with the appropriate amount of energy caused one of the electrons to jump to the next orbit.

An electron from the electron beam joined the helium electron, leading to the formation of a helium anion, which is highly reactive. These electrons can jump to targets that have a suitable size. The temperature as low as 0.4K in the helium droplets is suspected to aid the pairing of two electrons. This reaction is similar to how electron pairs behave in superconductors.

This study has been published in Angewandte Chemie.

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