Experimental determination of the interaction potential between a helium atom and the interior surface of a C60 fullerene molecule.

Anthony J Horsewill,Tanzeeha Jafari,Stéphane Rols,Jyrki Rantaharju,Malcolm H Levitt,Anna Shugai,Mohamed Aouane,Mark Walkey,Gabriela Hoffman,Toomas Rõõm,Richard J Whitby,Monica Jiménez-Ruiz,George Razvan Bacanu,Urmas Nagel

doi:10.1063/5.0066817

Abstract

The interactions between atoms and molecules may be described by a potential energy function of the nuclear coordinates. Nonbonded interactions between neutral atoms or molecules are dominated by repulsive forces at a short range and attractive dispersion forces at a medium range. Experimental data on the detailed interaction potentials for nonbonded interatomic and intermolecular forces are scarce. Here, we use terahertz spectroscopy and inelastic neutron scattering to determine the potential energy function for the nonbonded interaction between single He atoms and encapsulating C60 fullerene cages in the helium endofullerenes 3He@C60 and 4He@C60, synthesized by molecular surgery techniques. The experimentally derived potential is compared to estimates from quantum chemistry calculations and from sums of empirical two-body potentials.

Highlights

Nonbonded intermolecular interactions determine the structure and properties of most forms of matter
The experimentally derived potential is compared to estimates from quantum chemistry calculations and from sums of empirical two-body potentials
We have showed that the quantized energy levels of helium atoms encapsulated in C60 cages may be probed by THz spectroscopy and INS, despite the weak interactions of the He atoms with the electromagnetic field and with neutrons

Summary

Introduction

Nonbonded intermolecular interactions determine the structure and properties of most forms of matter. The potential energy function specifies the dependence of the potential energy on the nuclear coordinates of the interacting moieties within the Born–Oppenheimer approximation.. The estimation of potential functions for nonbonded interactions remains an active research area of computational chemistry.. Ab initio methods are capable of high accuracy but are usually too computationally expensive to be applied to anything but very small molecular systems. Computational techniques with good scaling properties, such as density functional theory (DFT), are generally imprecise for nonbonded interactions, unless customized adjustments are made.. The accuracy of quantum chemistry algorithms is often assessed by seeking convergence with respect to the calculation level or number of basis functions. Computational techniques with good scaling properties, such as density functional theory (DFT), are generally imprecise for nonbonded interactions, unless customized adjustments are made. The accuracy of quantum chemistry algorithms is often assessed by seeking convergence with respect to the calculation level or number of basis functions.

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Conclusion