Symmetry-breaking in the H2@C60 endofullerene revealed by inelastic neutron scattering at low temperature

Abstract

The fine structure of the rotational ground state of molecular ortho-hydrogen confined inside the fullerene cage C60 is investigated by inelastic neutron scattering (INS). The INS line corresponding to transitions between the three sub-levels comprising the ortho ground state to the non-degenerate para ground state was studied as a function of temperature down to 60 mK in neutron energy gain. The experiments show that at ambient pressure the three ortho sub-levels are split into a low energy non-degenerate level and a high energy doubly degenerate level separated by 0.135 ± 0.010 meV. This observation is consistent with hydrogen molecules being located at sites with axial symmetry superseding the icosahedral symmetry of isolated rigid C60 cages in the solid phase. To gain insight into the role of inter-cage interactions in determining the symmetry breaking potential, the effects of hydrostatic pressure on the fine structure of the line was also investigated. The analysis of the INS spectra shows that the potential and the energy levels of H2 are sensitive to the orientation of neighbouring cages, consistent with the low-temperature crystalline phase of C60.

Citation

Mamone, S., Johnson, M. R., Ollivier, J., Rols, S., Levitt, M. H., & Horsewill, A. J. (in press). Symmetry-breaking in the H2@C60 endofullerene revealed by inelastic neutron scattering at low temperature. Physical Chemistry Chemical Physics, 18(3), 1998-2005. https://doi.org/10.1039/c5cp07146a

• Journal Article Type: Article
• Acceptance Date: Dec 11, 2015
• Online Publication Date: Dec 11, 2015
• Deposit Date: Jul 13, 2016
• Publicly Available Date: Jul 13, 2016
• Journal: Physical Chemistry Chemical Physics
• Print ISSN: 1463-9076
• Electronic ISSN: 1463-9084
• Publisher: Royal Society of Chemistry
• Peer Reviewed: Peer Reviewed
• Volume: 18
• Issue: 3
• Pages: 1998-2005
• DOI: https://doi.org/10.1039/c5cp07146a
• Public URL: https://nottingham-repository.worktribe.com/output/769492
• Publisher URL: http://dx.doi.org/10.1039/c5cp07146a
• Additional Information: : This document is Similarity Check deposited; : The PCCP Owner Societies have an exclusive publication licence for this journal; OPEN ACCESS: This article is freely available. This article is licensed under a Creative Commons Attribution 3.0 Unported Licence (CC BY 3.0); : Single-blind; : Received 20 November 2015; Accepted 11 December 2015; Accepted Manuscript published 11 December 2015; Advance Article published 21 December 2015; Version of Record published 8 January 2016