The Endofullerene HF@C₆₀: Inelastic Neutron Scattering Spectra from Quantum Simulations and Experiment, Validity of the Selection Rule, and Symmetry Breaking

Abstract

Accurate quantum simulations of the low-temperature inelastic neutron scattering (INS) spectra of HF@C 60 are reported, for two incident neutron wavelengths. They are distinguished by the rigorous inclusion of symmetry-breaking effects in the treatment, and having the spectra computed with HF as the guest, rather than H 2 or HD, as in the past work. The results demonstrate that the precedent-setting INS selection rule, originally derived for H 2 and HD in near-spherical nanocavities, applies also to HF@C 60 , despite the large mass asymmetry of HF and the strongly mixed character of its translation-rotation eigenstates. This lends crucial support to the theoretical prediction [ Xu, M.; et al. J. Phys. Chem. Lett. 2015, 6, 3721] that the INS selection rule is valid for any diatomic molecule in near-spherical nanoconfinement. The selection rule remains valid in the presence of symmetry breaking, but is modified slightly in an interesting way. Comparison is made with the recently published experimental INS spectrum of HF@C 60. The agreement is very good, apart from one peak for which our calculations suggest a reassignment. This reassignment is consistent with the measured INS spectrum presented in this work, that covers an extended energy range. Graphical TOC Entry Theoretical (black) and measured INS spectra of HF@C 60 , with assignments.

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

“…22,32,34,41,43 The quantum structure has been studied in detail using models of the confining potential, sometimes combined with cage-induced modifications of the rotational and vibrational characteristics of the guest molecule. 32,33,35,36,[43][44][45][46][47][48][49][50][51][52][53][54][55][56] There are two main ways to describe the interaction potential between the encapsulated species and the cage. One approach describes the interaction potential as a sum over many two-body Lennard-Jones (LJ) functions involving each endohedral atom and all 60 carbon atoms of the cage, [44][45][46]49,50,52,53,55,56 sometimes introducing "additional sites" on the endohedral species as well.…”

A combined inelastic neutron scattering and simulation study of the 3He@C60 endofullerene

“…[22][23][24] Alongside these experimental investigations, numerical calculations have been used to compute the INS spectrum for various endofullerenes. [25][26][27][28][29] These calculations were crucial to understand the features observed experimentally, showing the necessity of performing simulations to understand neutron scattering spectra. 30 Noble gas endofullerenes 3,8,31 represent the simplest molecular arrangement in the endofullerene family.…”

Computational Energy Spectra of the H2O@C70 Endofullerene

“…The quantum behavior of the inner molecule has been investigated by using spectroscopic techniques, with the structures providing an isolated environment where peculiar quantum features can arise [12,15–19] . The study of an embedded water molecule can be done in such privileged conditions, and it is particularly interesting for the critical role played by water in a wide range of chemical and biological phenomena, with direct implications ranging from fundamental research to applied technologies [4,20–24] .…”

“…[14] The quantum behavior of the inner molecule has been investigated by using spectroscopic techniques, with the structures providing an isolated environment where peculiar quantum features can arise. [12,[15][16][17][18][19] The study of an embedded water molecule can be done in such privileged conditions, and it is particularly interesting for the critical role played by water in a wide range of chemical and biological phenomena, with direct implications ranging from fundamental research to applied technologies. [4,[20][21][22][23][24] In particular, a better understanding of the hydrogen bonds of water clusters and liquid water can be achieved if simple well-defined systems were available to study, as in the case of a water dimer in the inner space of C 60 and C 70 fullerenes.…”