Terahertz spectroscopy study of the confining potential for methane in the endofullerene CH₄@C₆₀

Abstract

We used terahertz spectroscopy to study the non-covalent interaction between CH₄ and the confining fullerene cage in endofullerene CH₄@C₆₀. The temperature dependence of the THz absorption spectra of powdered CH₄@C₆₀ was measured between 5 and 300 K. At temperatures below 50 K, the THz spectrum of CH₄ shows a single line centered at 214 cm⁻¹, which broadens and shifts to higher energy as the temperature increases. These effects are explained by the anharmonicity of the CH₄–C₆₀ interaction potential function. The model involves the center-of-mass motion of CH₄ in a spherically symmetric potential well. Line intensities are modeled by invoking an electric dipole moment induced by the translational displacement of CH₄ from the center of the cage C₆₀. The potential function and the dipole moment parameters were derived from the temperature dependence of the THz absorption spectra and compared with the parameters of previously studied endofullerenes. The quantum chemistry calculations reproduce the CH₄ translation motion frequency and the potential function remarkably well.

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ORCID for Sally Bloodworth: orcid.org/0000-0003-2219-3635

ORCID for Malcolm H. Levitt: orcid.org/0000-0001-9878-1180

ORCID for Richard J. Whitby: orcid.org/0000-0002-9891-5502

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