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Moncada F, Quintero W, Posada E, Pettersson LGM, Reyes A. A nuclear configuration interaction approach to study nuclear spin effects: an application to ortho- and para- 3 He 2 @C 60. Chemphyschem 2024; 25:e202300498. [PMID: 38055206 DOI: 10.1002/cphc.202300498] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2023] [Revised: 11/29/2023] [Accepted: 12/01/2023] [Indexed: 12/07/2023]
Abstract
We introduce a non-orthogonal configuration interaction approach to investigate nuclear quantum effects on energies and densities of confined fermionic nuclei. The Hamiltonian employed draws parallels between confined systems and many-electron atoms, where effective non-Coulombic potentials represent the interactions of the trapped particles. One advantage of this method is its generality, as it offers the potential to study the nuclear quantum effects of various confined species affected by effective isotropic or anisotropic potentials. As a first application, we analyze the quantum states of two 3 He atoms encapsulated in C60 . At the Hartree-Fock level, we observe the breaking of spin and spatial symmetries. To ensure wavefunctions with the correct symmetries, we mix the broken-symmetry Hartree-Fock states within the non-orthogonal configuration interaction expansion. Our proposed approach predicts singly and triply degenerate ground states for the singlet (para-3 He2 @C60 ) and triplet (ortho-3 He2 @C60 ) nuclear spin configurations, respectively. The ortho-3 He2 @C60 ground state is 5.69 cm-1 higher in energy than the para-3 He2 @C60 ground state. The nuclear densities obtained for these states exhibit the icosahedral symmetry of the C60 embedding potential. Importantly, our calculated energies for the lowest 85 states are in close agreement with perturbation theory results based on a harmonic oscillator plus rigid rotor model of 3 He2 @C60 .
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Affiliation(s)
- Félix Moncada
- Department of Physics, AlbaNova University Center, Stockholm University, 106 91, Stockholm, Sweden
- Department of Chemistry, Universidad Nacional de Colombia, Av. Cra 30 45-03, Bogotá, Colombia
| | - William Quintero
- Doctorado en Fisicoquímica Molecular, Universidad Andres Bello, Santiago de Chile, Chile
- Department of Chemistry, Universidad Nacional de Colombia, Av. Cra 30 45-03, Bogotá, Colombia
| | - Edwin Posada
- Institute for Computational Molecular Science, Temple University, Philadelphia, PA, USA
- Department of Chemistry, Universidad Nacional de Colombia, Av. Cra 30 45-03, Bogotá, Colombia
| | - Lars G M Pettersson
- Department of Physics, AlbaNova University Center, Stockholm University, 106 91, Stockholm, Sweden
| | - Andrés Reyes
- Department of Chemistry, Universidad Nacional de Colombia, Av. Cra 30 45-03, Bogotá, Colombia
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2
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Hyeon-Deuk K, Chang IY. Real-time hydrogen molecular dynamics satisfying the nuclear spin statistics of a quantum rotor. Commun Chem 2022; 5:168. [PMID: 36697851 DOI: 10.1038/s42004-022-00788-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2022] [Accepted: 11/24/2022] [Indexed: 12/07/2022] Open
Abstract
Apparent presence of the nuclear-spin species of a hydrogen molecule, para-hydrogen and ortho-hydrogen, associated with the quantum rotation is a manifestation of the nuclear quantum nature of hydrogen, governing not only molecular structures but also physical and chemical properties of hydrogen molecules. It has been a great challenge to observe and calculate real-time dynamics of such molecularized fermions. Here, we developed the non-empirical quantum molecular dynamics method that enables real-time molecular dynamics simulations of hydrogen molecules satisfying the nuclear spin statistics of the quantum rotor. While reproducing the species-dependent quantum rotational energy, population ratio, specific heat, and H-H bond length and frequency, we found that their translational, orientational and vibrational dynamics becomes accelerated with the higher rotational excitation, concluding that the nuclear quantum rotation stemmed from the nuclear spin statistics can induce various kinds of dynamics and reactions intrinsic to each hydrogen species.
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3
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Subhani M, Zhou J, Sui Y, Zou H, Frunzi M, Cross J, Saunders M, Shuai C, Liang W, Xu H. Reversible Diels–Alder Addition to Fullerenes: A Study of Dimethylanthracene with H2@C60. Nanomaterials 2022; 12:1667. [PMID: 35630891 PMCID: PMC9144212 DOI: 10.3390/nano12101667] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/30/2022] [Revised: 04/25/2022] [Accepted: 04/29/2022] [Indexed: 01/27/2023]
Abstract
The study of isolated atoms or molecules inside a fullerene cavity provides a unique environment. It is likely to control the outer carbon cage and study the isolated species when molecules or atoms are trapped inside a fullerene. We report the Diels–Alder addition reaction of 9,10-dimethyl anthracene (DMA) to H2@C60 while 1H NMR spectroscopy is utilized to characterize the Diels–Alder reaction of the DMA with the fullerene. Through 1H NMR spectroscopy, a series of isomeric adducts are identified. The obtained peaks are sharp, precise, and straightforward. Moreover, in this paper, H2@C60 and its isomers are described for the first time.
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4
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Jafari T, Razvan Bacanu G, Shugai A, Nagel U, Walkey M, Hoffman G, Levitt MH, Whitby RJ, Rõõm T. Terahertz spectroscopy of the helium endofullerene He@C 60. Phys Chem Chem Phys 2022; 24:9943-9952. [PMID: 35445229 DOI: 10.1039/d2cp00515h] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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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Affiliation(s)
- Tanzeeha Jafari
- National Institute of Chemical Physics and Biophysics, Akadeemia tee 23, Tallinn 12618, Estonia.
| | | | - Anna Shugai
- National Institute of Chemical Physics and Biophysics, Akadeemia tee 23, Tallinn 12618, Estonia.
| | - Urmas Nagel
- National Institute of Chemical Physics and Biophysics, Akadeemia tee 23, Tallinn 12618, Estonia.
| | - Mark Walkey
- School of Chemistry, University of Southampton, SO17 1BJ Southampton, UK
| | - Gabriela Hoffman
- School of Chemistry, University of Southampton, SO17 1BJ Southampton, UK
| | - Malcolm H Levitt
- School of Chemistry, University of Southampton, SO17 1BJ Southampton, UK
| | - Richard J Whitby
- School of Chemistry, University of Southampton, SO17 1BJ Southampton, UK
| | - Toomas Rõõm
- National Institute of Chemical Physics and Biophysics, Akadeemia tee 23, Tallinn 12618, Estonia.
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5
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Bacanu GR, Jafari T, Aouane M, Rantaharju J, Walkey M, Hoffman G, Shugai A, Nagel U, Jiménez-Ruiz M, Horsewill AJ, Rols S, Rõõm T, Whitby RJ, Levitt MH. Experimental determination of the interaction potential between a helium atom and the interior surface of a C 60 fullerene molecule. J Chem Phys 2021; 155:144302. [PMID: 34654304 DOI: 10.1063/5.0066817] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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.
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Affiliation(s)
- George Razvan Bacanu
- School of Chemistry, University of Southampton, Southampton SO17 1BJ, United Kingdom
| | - Tanzeeha Jafari
- National Institute of Chemical Physics and Biophysics, Tallinn 12618, Estonia
| | | | - Jyrki Rantaharju
- School of Chemistry, University of Southampton, Southampton SO17 1BJ, United Kingdom
| | - Mark Walkey
- School of Chemistry, University of Southampton, Southampton SO17 1BJ, United Kingdom
| | - Gabriela Hoffman
- School of Chemistry, University of Southampton, Southampton SO17 1BJ, United Kingdom
| | - Anna Shugai
- National Institute of Chemical Physics and Biophysics, Tallinn 12618, Estonia
| | - Urmas Nagel
- National Institute of Chemical Physics and Biophysics, Tallinn 12618, Estonia
| | | | - Anthony J Horsewill
- School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, United Kingdom
| | - Stéphane Rols
- Institut Laue-Langevin, BP 156, 38042 Grenoble, France
| | - Toomas Rõõm
- National Institute of Chemical Physics and Biophysics, Tallinn 12618, Estonia
| | - Richard J Whitby
- School of Chemistry, University of Southampton, Southampton SO17 1BJ, United Kingdom
| | - Malcolm H Levitt
- School of Chemistry, University of Southampton, Southampton SO17 1BJ, United Kingdom
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Hoffman G, Walkey MC, Gräsvik J, Bacanu GR, Alom S, Bloodworth S, Light ME, Levitt MH, Whitby RJ. A Solid‐State Intramolecular Wittig Reaction Enables Efficient Synthesis of Endofullerenes Including Ne@C
60
,
3
He@C
60
, and HD@C
60. Angew Chem Int Ed Engl 2021. [DOI: 10.1002/ange.202100817] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- Gabriela Hoffman
- Chemistry, Faculty of Engineering and Physical Sciences University of Southampton Southampton SO17 1BJ UK
| | - Mark C. Walkey
- Chemistry, Faculty of Engineering and Physical Sciences University of Southampton Southampton SO17 1BJ UK
| | - John Gräsvik
- Chemistry, Faculty of Engineering and Physical Sciences University of Southampton Southampton SO17 1BJ UK
- Current address: Iggesund Paperboard AB Iggesunds Bruk LSKA 82580 Iggesund Sweden
| | - George R. Bacanu
- Chemistry, Faculty of Engineering and Physical Sciences University of Southampton Southampton SO17 1BJ UK
| | - Shamim Alom
- Chemistry, Faculty of Engineering and Physical Sciences University of Southampton Southampton SO17 1BJ UK
| | - Sally Bloodworth
- Chemistry, Faculty of Engineering and Physical Sciences University of Southampton Southampton SO17 1BJ UK
| | - Mark E. Light
- Chemistry, Faculty of Engineering and Physical Sciences University of Southampton Southampton SO17 1BJ UK
| | - Malcolm H. Levitt
- Chemistry, Faculty of Engineering and Physical Sciences University of Southampton Southampton SO17 1BJ UK
| | - Richard J. Whitby
- Chemistry, Faculty of Engineering and Physical Sciences University of Southampton Southampton SO17 1BJ UK
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7
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Shugai A, Nagel U, Murata Y, Li Y, Mamone S, Krachmalnicoff A, Alom S, Whitby RJ, Levitt MH, Rõõm T. Infrared spectroscopy of an endohedral water in fullerene. J Chem Phys 2021; 154:124311. [PMID: 33810704 DOI: 10.1063/5.0047350] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
An infrared absorption spectroscopy study of the endohedral water molecule in a solid mixture of H2O@C60 and C60 was carried out at liquid helium temperature. From the evolution of the spectra during the ortho-para conversion process, the spectral lines were identified as para-H2O and ortho-H2O transitions. Eight vibrational transitions with rotational side peaks were observed in the mid-infrared: ω1, ω2, ω3, 2ω1, 2ω2, ω1 + ω3, ω2 + ω3, and 2ω2 + ω3. The vibrational frequencies ω2 and 2ω2 are lower by 1.6% and the rest by 2.4%, as compared to those of free H2O. A model consisting of a rovibrational Hamiltonian with the dipole and quadrupole moments of H2O interacting with the crystal field was used to fit the infrared absorption spectra. The electric quadrupole interaction with the crystal field lifts the degeneracy of the rotational levels. The finite amplitudes of the pure v1 and v2 vibrational transitions are consistent with the interaction of the water molecule dipole moment with a lattice-induced electric field. The permanent dipole moment of encapsulated H2O is found to be 0.50 ± 0.05 D as determined from the far-infrared rotational line intensities. The translational mode of the quantized center-of-mass motion of H2O in the molecular cage of C60 was observed at 110 cm-1 (13.6 meV).
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Affiliation(s)
- A Shugai
- National Institute of Chemical Physics and Biophysics, Akadeemia tee 23, 12618 Tallinn, Estonia
| | - U Nagel
- National Institute of Chemical Physics and Biophysics, Akadeemia tee 23, 12618 Tallinn, Estonia
| | - Y Murata
- Institute for Chemical Research, Kyoto University, Kyoto 611-0011, Japan
| | - Yongjun Li
- Department of Chemistry, Columbia University, New York, New York 10027, USA
| | - S Mamone
- School of Chemistry, Southampton University, Southampton SO17 1BJ, United Kingdom
| | - A Krachmalnicoff
- School of Chemistry, Southampton University, Southampton SO17 1BJ, United Kingdom
| | - S Alom
- School of Chemistry, Southampton University, Southampton SO17 1BJ, United Kingdom
| | - R J Whitby
- School of Chemistry, Southampton University, Southampton SO17 1BJ, United Kingdom
| | - M H Levitt
- School of Chemistry, Southampton University, Southampton SO17 1BJ, United Kingdom
| | - T Rõõm
- National Institute of Chemical Physics and Biophysics, Akadeemia tee 23, 12618 Tallinn, Estonia
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8
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Hoffman G, Walkey MC, Gräsvik J, Bacanu GR, Alom S, Bloodworth S, Light ME, Levitt MH, Whitby RJ. A Solid-State Intramolecular Wittig Reaction Enables Efficient Synthesis of Endofullerenes Including Ne@C 60 , 3 He@C 60 , and HD@C 60. Angew Chem Int Ed Engl 2021; 60:8960-8966. [PMID: 33554419 PMCID: PMC8048630 DOI: 10.1002/anie.202100817] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2021] [Indexed: 11/24/2022]
Abstract
An open‐cage fullerene incorporating phosphorous ylid and carbonyl group moieties on the rim of the orifice can be filled with gases (H2, He, Ne) in the solid state, and the cage opening then contracted in situ by raising the temperature to complete an intramolecular Wittig reaction, trapping the atom or molecule inside. Known transformations complete conversion of the product fullerene to C60 containing the endohedral species. As well as providing an improved synthesis of large quantities of 4He@C60, H2@C60, and D2@C60, the method allows the efficient incorporation of expensive gases such as HD and 3He, to prepare HD@C60 and 3He@C60. The method also enables the first synthesis of Ne@C60 by molecular surgery, and its characterization by crystallography and 13C NMR spectroscopy.
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Affiliation(s)
- Gabriela Hoffman
- Chemistry, Faculty of Engineering and Physical Sciences, University of Southampton, Southampton, SO17 1BJ, UK
| | - Mark C Walkey
- Chemistry, Faculty of Engineering and Physical Sciences, University of Southampton, Southampton, SO17 1BJ, UK
| | - John Gräsvik
- Chemistry, Faculty of Engineering and Physical Sciences, University of Southampton, Southampton, SO17 1BJ, UK.,Current address: Iggesund Paperboard AB, Iggesunds Bruk, LSKA, 82580, Iggesund, Sweden
| | - George R Bacanu
- Chemistry, Faculty of Engineering and Physical Sciences, University of Southampton, Southampton, SO17 1BJ, UK
| | - Shamim Alom
- Chemistry, Faculty of Engineering and Physical Sciences, University of Southampton, Southampton, SO17 1BJ, UK
| | - Sally Bloodworth
- Chemistry, Faculty of Engineering and Physical Sciences, University of Southampton, Southampton, SO17 1BJ, UK
| | - Mark E Light
- Chemistry, Faculty of Engineering and Physical Sciences, University of Southampton, Southampton, SO17 1BJ, UK
| | - Malcolm H Levitt
- Chemistry, Faculty of Engineering and Physical Sciences, University of Southampton, Southampton, SO17 1BJ, UK
| | - Richard J Whitby
- Chemistry, Faculty of Engineering and Physical Sciences, University of Southampton, Southampton, SO17 1BJ, UK
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9
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Bačić Z, Vlček V, Neuhauser D, Felker PM. Effects of symmetry breaking on the translation-rotation eigenstates of H 2, HF, and H 2O inside the fullerene C 60. Faraday Discuss 2018; 212:547-567. [PMID: 30226507 DOI: 10.1039/c8fd00082d] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Splittings of the translation-rotation (TR) eigenstates of the solid light-molecule endofullerenes M@C60 (M = H2, H2O, HF) attributed to the symmetry breaking have been observed in the infrared (IR) and inelastic neutron scattering spectra of these species in the past couple of years. In a recent paper [Felker et al., Phys. Chem. Chem. Phys., 2017, 19, 31274], we established that the electrostatic, quadrupolar interaction between the guest molecule M and the twelve nearest-neighbor C60 cages of the solid is the main source of the symmetry breaking. The splittings of the three-fold degenerate ground states of the endohedral ortho-H2, ortho-H2O and the j = 1 level of HF calculated using this model were found to be in excellent agreement with the experimental results. Utilizing the same electrostatic model, this theoretical study investigates the effects of the symmetry breaking on the excited TR eigenstates of the three species, and how they manifest in their simulated low-temperature (5-6 K) near-IR (NIR) and far-IR (FIR) spectra. The TR eigenstates are calculated variationally for both the major P and minor H crystal orientations. For the H orientation, the calculated splittings of all of the TR levels of these species are less than 0.1 cm-1. For the dominant P orientation, the splittings vary strongly depending on the character of the excitations involved. In all of the species, the splittings of the higher rotationally excited levels are comparable in magnitude to those for the j = 1 levels. For the levels corresponding to purely translational excitations, the calculated splittings are about an order of magnitude smaller than those of the purely rotational eigenstates. Based on the computed TR eigenstates, the low-temperature NIR (for M = H2) and FIR (for M = HF and H2O) spectra are simulated for both the P and H orientations, and also combined as their weighted sum (0.15H + 0.85P). The weighted sum spectra computed for M = H2 and HF match quantitatively the corresponding measured spectra, while for M = H2O, the weighted sum FIR spectrum predicts features that can potentially be observed experimentally.
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Affiliation(s)
- Zlatko Bačić
- Department of Chemistry, New York University, New York, NY 10003, USA. and NYU-ECNU Center for Computational Chemistry at NYU Shanghai, 3663 Zhongshan Road North, Shanghai, 200062, China
| | - Vojtěch Vlček
- Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095-1569, USA.
| | - Daniel Neuhauser
- Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095-1569, USA.
| | - Peter M Felker
- Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095-1569, USA.
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10
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Bačić Z. Perspective: Accurate treatment of the quantum dynamics of light molecules inside fullerene cages: Translation-rotation states, spectroscopy, and symmetry breaking. J Chem Phys 2018; 149:100901. [PMID: 30219006 DOI: 10.1063/1.5049358] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
In this perspective, I review the current status of the theoretical investigations of the quantum translation-rotation (TR) dynamics and spectroscopy of light molecules encapsulated inside fullerenes, mostly C60 and C70. The methodologies developed in the past decade allow accurate quantum calculations of the TR eigenstates of one and two nanoconfined molecules and have led to deep insights into the nature of the underlying dynamics. Combining these bound-state methodologies with the formalism of inelastic neutron scattering (INS) has resulted in the novel and powerful approach for the quantum calculation of the INS spectra of a diatomic molecule in a nanocavity with an arbitrary geometry. These simulations have not only become indispensable for the interpretation and assignment of the experimental spectra but are also behind the surprising discovery of the INS selection rule for diatomics in near-spherical nanocavities. Promising directions for future research are discussed.
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Affiliation(s)
- Zlatko Bačić
- Department of Chemistry, New York University, New York, New York 10003, USA
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11
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Chojecki M, Yourdkhani S, Rutkowska-zbik D, Korona T. Stability of endo- and exohedral complexes of all-boron fullerene B 40. COMPUT THEOR CHEM 2018; 1133:7-17. [DOI: 10.1016/j.comptc.2018.04.007] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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12
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Abstract
To investigate the effect of quantum fluctuations on the magnetic environment inside a C60 fullerene cage, we have calculated the nuclear magnetic shielding constant of protons in H2@C60 and HD@C60 systems by on-the-fly ab initio path integral simulation, including both thermal and nuclear quantum effects. The most dominant upfield from an isolated hydrogen molecule occurs due to the diamagnetic current of the C60 cage, which is partly cancelled by the paramagnetic current, where the paramagnetic contribution is enlarged by the zero-point vibrational fluctuation of the C60 carbon backbone structure via a widely distributed HOMO-LUMO gap. This quantum modulation mechanism of the nuclear magnetic shielding constant is newly proposed. Because this quantum effect is independent of the difference between H2 and HD, the H2/HD isotope shift occurs in spite of the C60 cage. The nuclear magnetic constants computed for H2@C60 and HD@C60 are 32.047 and 32.081 ppm, respectively, which are in reasonable agreement with the corresponding values of 32.19 and 32.23 ppm estimated from the experimental values of the chemical shifts.
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Affiliation(s)
- Tsutomu Kawatsu
- Graduate School of Nanobioscience, Yokohama City University, 22-2 Seto, Kanazawa-ku, Yokohama 236-0027, Japan.
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13
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Kalugina YN, Roy PN. Potential energy and dipole moment surfaces for HF@C60: Prediction of spectral and electric response properties. J Chem Phys 2017; 147:244303. [DOI: 10.1063/1.5006589] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Yulia N. Kalugina
- Department of Chemistry, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada
| | - Pierre-Nicholas Roy
- Department of Chemistry, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada
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14
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Felker PM, Bačić Z. Accurate quantum calculations of translation-rotation eigenstates in electric-dipole-coupled H2O@C60 assemblies. Chem Phys Lett 2017. [DOI: 10.1016/j.cplett.2017.02.027] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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15
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Felker PM, Bačić Z. Electric-dipole-coupled H2O@C60 dimer: Translation-rotation eigenstates from twelve-dimensional quantum calculations. J Chem Phys 2017; 146:084303. [DOI: 10.1063/1.4976526] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Peter M. Felker
- Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095-1569, USA
| | - Zlatko Bačić
- Department of Chemistry, New York University, New York, New York 10003, USA
- NYU-ECNU Center for Computational Chemistry at NYU Shanghai, 3663 Zhongshan Road North, Shanghai 200062, China
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16
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Felker PM, Vlček V, Hietanen I, FitzGerald S, Neuhauser D, Bačić Z. Explaining the symmetry breaking observed in the endofullerenes H2@C60, HF@C60, and H2O@C60. Phys Chem Chem Phys 2017; 19:31274-31283. [DOI: 10.1039/c7cp06062a] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Symmetry breaking has been recently observed in the endofullerenes M@C60 (M = H2, HF, H2O), manifesting in the splittings of the three-fold degenerate ground states of the endohedral ortho-H2, ortho-H2O and the j = 1 level of HF.
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Affiliation(s)
- Peter M. Felker
- Department of Chemistry and Biochemistry
- University of California
- Los Angeles
- USA
| | - Vojtěch Vlček
- Department of Chemistry and Biochemistry
- University of California
- Los Angeles
- USA
| | - Isaac Hietanen
- Department of Physics and Astronomy
- Oberlin College
- Oberlin
- USA
| | | | - Daniel Neuhauser
- Department of Chemistry and Biochemistry
- University of California
- Los Angeles
- USA
| | - Zlatko Bačić
- Department of Chemistry
- New York University
- New York
- USA
- NYU-ECNU Center for Computational Chemistry at NYU Shanghai
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17
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Affiliation(s)
- Peter M. Felker
- Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095-1569, USA
| | - Zlatko Bačić
- Department of Chemistry, New York University, New York, New York 10003, USA
- NYU-ECNU Center for Computational Chemistry at NYU Shanghai, 3663 Zhongshan Road North, Shanghai 200062, China
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Krachmalnicoff A, Bounds R, Mamone S, Alom S, Concistrè M, Meier B, Kouřil K, Light ME, Johnson MR, Rols S, Horsewill AJ, Shugai A, Nagel U, Rõõm T, Carravetta M, Levitt MH, Whitby RJ. The dipolar endofullerene HF@C60. Nat Chem 2016; 8:953-7. [DOI: 10.1038/nchem.2563] [Citation(s) in RCA: 137] [Impact Index Per Article: 17.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2015] [Accepted: 05/25/2016] [Indexed: 12/22/2022]
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19
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Felker PM. Fully quantal calculation of H2 translation-rotation states in the (p-H2)2@51264 clathrate hydrate inclusion compound. J Chem Phys 2014; 141:184305. [DOI: 10.1063/1.4901057] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Equbal A, Srinivasan S, Ramachandran C, Sathyamurthy N. Encapsulation of paramagnetic diatomic molecules B 2 , O 2 and Ge 2 inside C 60. Chem Phys Lett 2014. [DOI: 10.1016/j.cplett.2014.07.031] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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21
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Goh KSK, Jiménez-Ruiz M, Johnson MR, Rols S, Ollivier J, Denning MS, Mamone S, Levitt MH, Lei X, Li Y, Turro NJ, Murata Y, Horsewill AJ. Symmetry-breaking in the endofullerene H2O@C60 revealed in the quantum dynamics of ortho and para-water: a neutron scattering investigation. Phys Chem Chem Phys 2014; 16:21330-9. [DOI: 10.1039/c4cp03272a] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The splitting of the ortho-H2O ground state is clearly revealed by inelastic neutron scattering.
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Affiliation(s)
- Kelvin S. K. Goh
- School of Physics & Astronomy
- University of Nottingham
- Nottingham NG7 2RD, UK
| | | | | | | | | | - Mark S. Denning
- School of Chemistry
- University of Southampton
- Southampton SO17 1BJ, UK
| | - Salvatore Mamone
- School of Chemistry
- University of Southampton
- Southampton SO17 1BJ, UK
| | - Malcolm H. Levitt
- School of Chemistry
- University of Southampton
- Southampton SO17 1BJ, UK
| | - Xuegong Lei
- Department of Chemistry
- Columbia University
- New York, USA
| | - Yongjun Li
- Department of Chemistry
- Columbia University
- New York, USA
| | | | - Yasujiro Murata
- Institute for Chemical Research
- Kyoto University
- Kyoto 611-0011, Japan
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22
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Abstract
New efficient and practical routes to H2O@C60, D2O@C60 and H2@C60 are described.
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Abstract
Magic-angle-spinning solid-state NMR provides site-resolved structural and chemical information about molecules that complements many other physical techniques. Recent technical advances have made it possible to perform magic-angle-spinning NMR experiments at low temperatures, allowing researchers to trap reaction intermediates and to perform site-resolved studies of low-temperature physical phenomena such as quantum rotations, quantum tunneling, ortho-para conversion between spin isomers, and superconductivity. In examining biological molecules, the improved sensitivity provided by cryogenic NMR facilitates the study of protein assembly or membrane proteins. The combination of low-temperatures with dynamic nuclear polarization has the potential to boost sensitivity even further. Many research groups, including ours, have addressed the technical challenges and developed hardware for magic-angle-spinning of samples cooled down to a few tens of degrees Kelvin. In this Account, we briefly describe these hardware developments and review several recent activities of our group which involve low-temperature magic-angle-spinning NMR. Low-temperature operation allows us to trap intermediates that cannot be studied under ambient conditions by NMR because of their short lifetime. We have used low-temperature NMR to study the electronic structure of bathorhodopsin, the primary photoproduct of the light-sensitive membrane protein, rhodopsin. This project used a custom-built NMR probe that allows low-temperature NMR in the presence of illumination (the image shows the illuminated spinner module). We have also used this technique to study the behavior of molecules within a restricted environment. Small-molecule endofullerenes are interesting molecular systems in which molecular rotors are confined to a well-insulated, well-defined, and highly symmetric environment. We discuss how cryogenic solid state NMR can give information on the dynamics of ortho-water confined in a fullerene cage. Molecular motions are often connected with fundamental chemical properties; therefore, an understanding of molecular dynamics can be important in fields ranging from material science to biochemistry. We present the case of ibuprofen sodium salt which exhibits different degrees of conformational freedom in different parts of the same molecule, leading to a range of line broadening and line narrowing phenomena as a function of temperature.
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Affiliation(s)
- Maria ConcistrÈ
- School of Chemistry, Southampton University, Southampton SO17 1BJ, United Kingdom
| | - Ole G. Johannessen
- School of Chemistry, Southampton University, Southampton SO17 1BJ, United Kingdom
| | - Elisa Carignani
- Dipartimento di Chimica e Chimica Industriale, Università di Pisa, Via Risorgimento 35, 56126, Pisa, Italy
| | - Marco Geppi
- Dipartimento di Chimica e Chimica Industriale, Università di Pisa, Via Risorgimento 35, 56126, Pisa, Italy
| | - Malcolm H. Levitt
- School of Chemistry, Southampton University, Southampton SO17 1BJ, United Kingdom
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Mamone S, Concistrè M, Heinmaa I, Carravetta M, Kuprov I, Wall G, Denning M, Lei X, Chen JYC, Li Y, Murata Y, Turro NJ, Levitt MH. Nuclear magnetic resonance of hydrogen molecules trapped inside C70 fullerene cages. Chemphyschem 2013; 14:3121-30. [PMID: 23788291 PMCID: PMC4068279 DOI: 10.1002/cphc.201300269] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2013] [Indexed: 11/29/2022]
Abstract
We present a solid-state NMR study of H2 molecules confined inside the cavity of C70 fullerene cages over a wide range of temperatures (300 K to 4 K). The proton NMR spectra are consistent with a model in which the dipole-dipole coupling between the ortho-H2 protons is averaged over the rotational/translational states of the confined quantum rotor, with an additional chemical shift anisotropy δ(H)(CSA)=10.1 ppm induced by the carbon cage. The magnitude of the chemical shift anisotropy is consistent with DFT estimates of the chemical shielding tensor field within the cage. The experimental NMR data indicate that the ground state of endohedral ortho-H2 in C70 is doubly degenerate and polarized transverse to the principal axis of the cage. The NMR spectra indicate significant magnetic alignment of the C70 long axes along the magnetic field, at temperatures below ~10 K.
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Affiliation(s)
- Salvatore Mamone
- School of Chemistry, Southampton University, Southampton SO17 1BJ (United Kingdom).
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Abstract
Molecular endofullerenes are supramolecular systems consisting of fullerene cages encapsulating small molecules. Although most early examples consist of encapsulated metal clusters, recently developed synthetic routes have provided endofullerenes with non-metallic guest molecules in high purity and macroscopic quantities. The encapsulated light molecule behaves as a confined quantum rotor, displaying rotational quantization as well as translational quantization, and a rich coupling between the translational and rotational degrees of freedom. Furthermore, many encapsulated molecules display spin isomerism. Spectroscopies such as inelastic neutron scattering, nuclear magnetic resonance and infrared spectroscopy may be used to obtain information on the quantized energy level structure and spin isomerism of the guest molecules. It is also possible to study the influence of the guest molecules on the cages, and to explore the communication between the guest molecules and the molecular environment outside the cage.
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Affiliation(s)
- Malcolm H Levitt
- School of Chemistry, University of Southampton, Highfield, Southampton SO17 1BJ, UK.
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26
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Filidou V, Mamone S, Simmons S, Karlen SD, Anderson HL, Kay CWM, Bagno A, Rastrelli F, Murata Y, Komatsu K, Lei X, Li Y, Turro NJ, Levitt MH, Morton JJL. Probing the C₆₀ triplet state coupling to nuclear spins inside and out. Philos Trans A Math Phys Eng Sci 2013; 371:20120475. [PMID: 23918718 DOI: 10.1098/rsta.2012.0475] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
The photoexcitation of functionalized fullerenes to their paramagnetic triplet electronic state can be studied by pulsed electron paramagnetic resonance (EPR) spectroscopy, whereas the interactions of this state with the surrounding nuclear spins can be observed by a related technique: electron nuclear double resonance (ENDOR). In this study, we present EPR and ENDOR studies on a functionalized exohedral fullerene system, dimethyl[9-hydro (C60-Ih)[5,6]fulleren-1(9H)-yl]phosphonate (DMHFP), where the triplet electron spin has been used to hyperpolarize, couple and measure two nuclear spins. We go on to discuss the extension of these methods to study a new class of endohedral fullerenes filled with small molecules, such as H₂@C₆₀, and we relate the results to density functional calculations.
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Affiliation(s)
- Vasileia Filidou
- London Centre for Nanotechnology, University College London, London WC1H 0AH, UK.
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Concistrè M, Mamone S, Denning M, Pileio G, Lei X, Li Y, Carravetta M, Turro NJ, Levitt MH. Anisotropic nuclear spin interactions in H₂O@C₆₀ determined by solid-state NMR. Philos Trans A Math Phys Eng Sci 2013; 371:20120102. [PMID: 23918716 DOI: 10.1098/rsta.2012.0102] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
We report a solid-state NMR study of the anisotropic nuclear spin interactions in H₂O@C₆₀ at room temperature. We find evidence of significant dipole-dipole interactions between the water protons, and also a proton chemical shift anisotropy (CSA) interaction. The principal axes of these interaction tensors are found to be perpendicular. The magnitude of the CSA is too large to be explained by a model in which the water molecules are partially aligned with respect to an external axis. The evidence indicates that the observed CSA is caused by a distortion of the geometry or electronic structure of the fullerene cages, in response to the presence of the endohedral water.
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Affiliation(s)
- M Concistrè
- School of Chemistry, University of Southampton, Highfield, Southampton SO17 1BJ, UK.
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Rõõm T, Peedu L, Ge M, Hüvonen D, Nagel U, Ye S, Xu M, Bačić Z, Mamone S, Levitt MH, Carravetta M, Chen JYC, Lei X, Turro NJ, Murata Y, Komatsu K. Infrared spectroscopy of small-molecule endofullerenes. Philos Trans A Math Phys Eng Sci 2013; 371:20110631. [PMID: 23918713 DOI: 10.1098/rsta.2011.0631] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Hydrogen is one of the few molecules that has been incarcerated in the molecular cage of C₆₀ to form the endohedral supramolecular complex H₂@C₆₀. In this confinement, hydrogen acquires new properties. Its translation motion, within the C₆₀ cavity, becomes quantized, is correlated with its rotation and breaks inversion symmetry that induces infrared (IR) activity of H₂. We apply IR spectroscopy to study the dynamics of hydrogen isotopologues H₂, D₂ and HD incarcerated in C₆₀. The translation and rotation modes appear as side bands to the hydrogen vibration mode in the mid-IR part of the absorption spectrum. Because of the large mass difference of hydrogen and C₆₀ and the high symmetry of C₆₀ the problem is almost identical to a vibrating rotor moving in a three-dimensional spherical potential. We derive potential, rotation, vibration and dipole moment parameters from the analysis of the IR absorption spectra. Our results were used to derive the parameters of a pairwise additive five-dimensional potential energy surface for H₂@C₆₀. The same parameters were used to predict H₂ energies inside C₇₀. We compare the predicted energies and the low-temperature IR absorption spectra of H₂@C₇₀.
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Affiliation(s)
- T Rõõm
- National Institute of Chemical Physics and Biophysics, Akadeemia tee 23, 12618 Tallinn, Estonia.
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Xu M, Ye S, Lawler R, Turro NJ, Bačić Z. HD in C₆₀: theoretical prediction of the inelastic neutron scattering spectrum and its temperature dependence. Philos Trans A Math Phys Eng Sci 2013; 371:20110630. [PMID: 23918712 DOI: 10.1098/rsta.2011.0630] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
We report rigorous quantum calculations of the inelastic neutron scattering (INS) spectra of HD@C₆₀, over a range of temperatures from 0 to 240 K and for two incident neutron wavelengths used in recent experimental investigations. The computations were performed using our newly developed methodology, which incorporates the coupled five-dimensional translation-rotation (T-R) eigenstates of the guest molecule as the initial and final states of the INS transitions, and yields highly detailed spectra. Depending on the incident neutron wavelength, the number of computed INS transitions varies from almost 500 to over 2000. The low-temperature INS spectra display the fingerprints of the coupling between the translational and rotational motions of the entrapped HD molecule, which is responsible for the characteristic splitting patterns of the T-R energy levels. INS transitions from the ground T-R state of HD to certain sublevels of excited T-R multiplets have zero intensity and are absent from the spectra. This surprising finding is explained by the new INS selection rule introduced here. The calculated spectra exhibit strong temperature dependence. As the temperature increases, numerous new peaks appear, arising from the transitions originating in excited T-R states which become populated. Our calculations show that the higher temperature features typically comprise two or more transitions close in energy and with similar intensities, interspersed with numerous other transitions whose intensities are negligible. This implies that accurately calculated energies and intensities of INS transitions which our methodology provides will be indispensable for reliable interpretation and assignment of the experimental spectra of HD@C₆₀ and related systems at higher temperatures.
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Affiliation(s)
- Minzhong Xu
- Department of Chemistry, New York University, New York, NY 10003, USA
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30
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Horsewill AJ, Goh K, Rols S, Ollivier J, Johnson MR, Levitt MH, Carravetta M, Mamone S, Murata Y, Chen JYC, Johnson JA, Lei X, Turro NJ. Quantum rotation and translation of hydrogen molecules encapsulated inside C₆₀: temperature dependence of inelastic neutron scattering spectra. Philos Trans A Math Phys Eng Sci 2013; 371:20110627. [PMID: 23918709 DOI: 10.1098/rsta.2011.0627] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
The quantum dynamics of a hydrogen molecule encapsulated inside the cage of a C60 fullerene molecule is investigated using inelastic neutron scattering (INS). The emphasis is on the temperature dependence of the INS spectra which were recorded using time-of-flight spectrometers. The hydrogen endofullerene system is highly quantum mechanical, exhibiting both translational and rotational quantization. The profound influence of the Pauli exclusion principle is revealed through nuclear spin isomerism. INS is shown to be exceptionally able to drive transitions between ortho-hydrogen and para-hydrogen which are spin-forbidden to photon spectroscopies. Spectra in the temperature range 1.6≤T≤280 K are presented, and examples are given which demonstrate how the temperature dependence of the INS peak amplitudes can provide an effective tool for assigning the transitions. It is also shown in a preliminary investigation how the temperature dependence may conceivably be used to probe crystal field effects and inter-fullerene interactions.
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Affiliation(s)
- A J Horsewill
- School of Physics and Astronomy, University of Nottingham, , Nottingham NG7 2RD, UK.
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31
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Xu M, Ye S, Powers A, Lawler R, Turro NJ, Bačić Z. Inelastic neutron scattering spectrum of H2@C60 and its temperature dependence decoded using rigorous quantum calculations and a new selection rule. J Chem Phys 2013; 139:064309. [DOI: 10.1063/1.4817534] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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Ye S, Xu M, FitzGerald S, Tchernyshyov K, Bačić Z. H2 in solid C60: Coupled translation-rotation eigenstates in the octahedral interstitial site from quantum five-dimensional calculations. J Chem Phys 2013; 138:244707. [DOI: 10.1063/1.4811220] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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33
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Abstract
The quantal translation-rotation states of two endohedral H(2) moieties in C(70) are computed by means of a nuclear-orbital/configuration-interaction method. H(2) "nuclear orbitals" are calculated as the translation-rotation eigenfunctions of one H(2) molecule interacting with C(70) and the mean field of the second H(2) molecule. Configurations are constructed as symmetrized bilinear products of these orbitals. These configurations are employed as the basis in which the matrix of the translation-rotation Hamiltonian of the cluster is computed and diagonalized. We show that this scheme allows for an efficient means to calculate the Hamiltonian matrix elements. We show that the configuration basis states represent excellent first approximations to the eigenstates of the species. Finally, we present results pertaining to the (H(2))(2)@C(70) low-energy translation-rotation level structure that can be understood in terms of a small number of H(2) excitation types.
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Affiliation(s)
- Peter M Felker
- Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095-1569, USA.
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Beduz C, Carravetta M, Chen JY, Concistrè M, Denning M, Frunzi M, Horsewill AJ, Johannessen OG, Lawler R, Lei X, Levitt MH, Li Y, Mamone S, Murata Y, Nagel U, Nishida T, Ollivier J, Rols S, Rõõm T, Sarkar R, Turro NJ, Yang Y. Quantum rotation of ortho and para-water encapsulated in a fullerene cage. Proc Natl Acad Sci U S A 2012; 109:12894-8. [PMID: 22837402 DOI: 10.1073/pnas.1210790109] [Citation(s) in RCA: 121] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Inelastic neutron scattering, far-infrared spectroscopy, and cryogenic nuclear magnetic resonance are used to investigate the quantized rotation and ortho-para conversion of single water molecules trapped inside closed fullerene cages. The existence of metastable ortho-water molecules is demonstrated, and the interconversion of ortho-and para-water spin isomers is tracked in real time. Our investigation reveals that the ground state of encapsulated ortho water has a lifted degeneracy, associated with symmetry-breaking of the water environment.
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