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Terahertz spectroscopy of the helium endofullerene He@C60

Terahertz spectroscopy of the helium endofullerene He@C60
Terahertz spectroscopy of the helium endofullerene He@C60
We studied the quantized translational motion of single He atoms encapsulated in molecular cages by terahertz absorption. The temperature dependence of the THz absorption spectra of 3He@C60 and 4He@C60 crystal powder samples was measured between 5 and 220 K. At 5 K there is an absorption line at 96.8 cm−1 (2.90 THz) in 3He@C60 and at 81.4 cm (2.44 THz) in 4He@C60, while additional absorption lines appear at higher temperature. An anharmonic spherical oscillator model with a displacement-induced dipole moment was used to model the absorption spectra. Potential energy terms with powers of two, four and six and induced dipole moment terms with powers one and three in the helium atom displacement from the fullerene cage center were sufficient to describe the experimental results. Excellent agreement is found between potential energy functions derived from measurements on the 3He and 4He isotopes. One absorption line corresponds to a three-quantum transition in 4He@C60, allowed by the anharmonicity of the potential function and by the non-linearity of the dipole moment in He atom displacement. The potential energy function of icosahedral symmetry does not explain the fine structure observed in the low temperature spectra.
1463-9076
9943-9952
Jafari, Tanzeeha
61ee9e84-ddd1-44fe-9f81-278019d45119
Razvan Bacanu, George
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Shugai, Anna
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Nagel, Urmas
18190a5a-a4c2-49d2-9a44-2ba31eb57655
Walkey, Mark
432139de-52cb-4e28-9ad0-b254e0523775
Hoffman, Gabriela
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Levitt, Malcolm H.
bcc5a80a-e5c5-4e0e-9a9a-249d036747c3
Whitby, Richard J.
45632236-ab00-4ad0-a02d-6209043e818b
Rõõm, Toomas
49325730-0d65-4f8a-b8b8-776696939cbc
Jafari, Tanzeeha
61ee9e84-ddd1-44fe-9f81-278019d45119
Razvan Bacanu, George
d2d1a581-2320-4bc6-b4cd-58d8334453fd
Shugai, Anna
919cb44b-125c-4f62-bd57-b9253615ab2b
Nagel, Urmas
18190a5a-a4c2-49d2-9a44-2ba31eb57655
Walkey, Mark
432139de-52cb-4e28-9ad0-b254e0523775
Hoffman, Gabriela
8b98ba1c-ee09-4922-82e4-a9240aa12e64
Levitt, Malcolm H.
bcc5a80a-e5c5-4e0e-9a9a-249d036747c3
Whitby, Richard J.
45632236-ab00-4ad0-a02d-6209043e818b
Rõõm, Toomas
49325730-0d65-4f8a-b8b8-776696939cbc

Jafari, Tanzeeha, Razvan Bacanu, George, Shugai, Anna, Nagel, Urmas, Walkey, Mark, Hoffman, Gabriela, Levitt, Malcolm H., Whitby, Richard J. and Rõõm, Toomas (2022) Terahertz spectroscopy of the helium endofullerene He@C60. Physical Chemistry Chemical Physics, 24 (17), 9943-9952. (doi:10.1039/d2cp00515h).

Record type: Article

Abstract

We studied the quantized translational motion of single He atoms encapsulated in molecular cages by terahertz absorption. The temperature dependence of the THz absorption spectra of 3He@C60 and 4He@C60 crystal powder samples was measured between 5 and 220 K. At 5 K there is an absorption line at 96.8 cm−1 (2.90 THz) in 3He@C60 and at 81.4 cm (2.44 THz) in 4He@C60, while additional absorption lines appear at higher temperature. An anharmonic spherical oscillator model with a displacement-induced dipole moment was used to model the absorption spectra. Potential energy terms with powers of two, four and six and induced dipole moment terms with powers one and three in the helium atom displacement from the fullerene cage center were sufficient to describe the experimental results. Excellent agreement is found between potential energy functions derived from measurements on the 3He and 4He isotopes. One absorption line corresponds to a three-quantum transition in 4He@C60, allowed by the anharmonicity of the potential function and by the non-linearity of the dipole moment in He atom displacement. The potential energy function of icosahedral symmetry does not explain the fine structure observed in the low temperature spectra.

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Accepted/In Press date: 3 April 2022
e-pub ahead of print date: 21 April 2022
Published date: 21 April 2022
Additional Information: Funding Information: This research was supported by the Estonian Ministry of Education and Research institutional research funding IUT23-3, Estonian Research Council grant PRG736, the European Regional Development Fund project TK134 and by EPSRC-UK, grant numbers EP/P009980/1 and EP/T004320/1. Publisher Copyright: © 2022 The Royal Society of Chemistry Copyright: Copyright 2022 Elsevier B.V., All rights reserved.

Identifiers

Local EPrints ID: 467636
URI: http://eprints.soton.ac.uk/id/eprint/467636
ISSN: 1463-9076
PURE UUID: 798ab539-ac5a-4dcd-bf16-2172ee593440
ORCID for Malcolm H. Levitt: ORCID iD orcid.org/0000-0001-9878-1180
ORCID for Richard J. Whitby: ORCID iD orcid.org/0000-0002-9891-5502

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Date deposited: 18 Jul 2022 16:51
Last modified: 18 Mar 2024 02:53

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Contributors

Author: Tanzeeha Jafari
Author: George Razvan Bacanu
Author: Anna Shugai
Author: Urmas Nagel
Author: Mark Walkey
Author: Gabriela Hoffman
Author: Toomas Rõõm

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