### Abstract

Recent synthesis of the endohedral complexes of C_{70} and its open-cage derivative with one and two H_{2} molecules has opened the path for experimental and theoretical investigations of the unique dynamic, spectroscopic, and other properties of systems with multiple hydrogen molecules confined inside a nanoscale cavity. Here we report a rigorous theoretical study of the dynamics of the coupled translational and rotational motions of H _{2} molecules in C_{70} and C_{60}, which are highly quantum mechanical. Diffusion Monte Carlo (DMC) calculations were performed for up to three para-H_{2} (p-H_{2}) molecules encapsulated in C_{70} and for one and two p-H_{2} molecules inside C _{60}. These calculations provide a quantitative description of the ground-state properties, energetics, and the translation-rotation (T-R) zero-point energies (ZPEs) of the nanoconfined p-H_{2} molecules and of the spatial distribution of two p-H_{2} molecules in the cavity of C_{70}. The energy of the global minimum on the intermolecular potential energy surface (PES) is negative for one and two H_{2} molecules in C_{70} but has a high positive value when the third H_{2} is added, implying that at most two H_{2} molecules can be stabilized inside C_{70}. By the same criterion, in the case of C_{60}, only the endohedral complex with one H_{2} molecule is energetically stable. Our results are consistent with the fact that recently both (H _{2})_{n}@C_{70} (n = 1, 2) and H_{2}@C _{60} were prepared, but not (H_{2})_{3}@C_{70} or (H_{2})_{2}@C_{60}. The ZPE of the coupled T-R motions, from the DMC calculations, grows rapidly with the number of caged p-H_{2} molecules and is a significant fraction of the well depth of the intermolecular PES, 11% in the case of p-H_{2}@C_{70} and 52% for (p-H_{2})_{2}@C_{70}. Consequently, the T-R ZPE represents a major component of the energetics of the encapsulated H_{2} molecules. The inclusion of the ZPE nearly doubles the energy by which (p-H_{2})_{3}@C_{70} is destabilized and increases by 66% the energetic destabilization of (p-H_{2})_{2}@C _{60}. For these reasons, the T-R ZPE has to be calculated accurately and taken into account for reliable theoretical predictions regarding the stability of the endohedral fullerene complexes with hydrogen molecules and their maximum H_{2} content.

Original language | English (US) |
---|---|

Pages (from-to) | 9826-9832 |

Number of pages | 7 |

Journal | Journal of the American Chemical Society |

Volume | 132 |

Issue number | 28 |

DOIs | |

State | Published - Jul 21 2010 |

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### ASJC Scopus subject areas

- Chemistry(all)
- Catalysis
- Biochemistry
- Colloid and Surface Chemistry

### Cite this

*Journal of the American Chemical Society*,

*132*(28), 9826-9832. https://doi.org/10.1021/ja103062g

**Hydrogen molecules inside fullerene C70 : Quantum dynamics, energetics, maximum occupancy, and comparison with C60.** / Sebastianelli, Francesco; Xu, Minzhong; Bacic, Zlatko; Lawler, Ronald; Turro, Nicholas J.

Research output: Contribution to journal › Article

*Journal of the American Chemical Society*, vol. 132, no. 28, pp. 9826-9832. https://doi.org/10.1021/ja103062g

}

TY - JOUR

T1 - Hydrogen molecules inside fullerene C70

T2 - Quantum dynamics, energetics, maximum occupancy, and comparison with C60

AU - Sebastianelli, Francesco

AU - Xu, Minzhong

AU - Bacic, Zlatko

AU - Lawler, Ronald

AU - Turro, Nicholas J.

PY - 2010/7/21

Y1 - 2010/7/21

N2 - Recent synthesis of the endohedral complexes of C70 and its open-cage derivative with one and two H2 molecules has opened the path for experimental and theoretical investigations of the unique dynamic, spectroscopic, and other properties of systems with multiple hydrogen molecules confined inside a nanoscale cavity. Here we report a rigorous theoretical study of the dynamics of the coupled translational and rotational motions of H 2 molecules in C70 and C60, which are highly quantum mechanical. Diffusion Monte Carlo (DMC) calculations were performed for up to three para-H2 (p-H2) molecules encapsulated in C70 and for one and two p-H2 molecules inside C 60. These calculations provide a quantitative description of the ground-state properties, energetics, and the translation-rotation (T-R) zero-point energies (ZPEs) of the nanoconfined p-H2 molecules and of the spatial distribution of two p-H2 molecules in the cavity of C70. The energy of the global minimum on the intermolecular potential energy surface (PES) is negative for one and two H2 molecules in C70 but has a high positive value when the third H2 is added, implying that at most two H2 molecules can be stabilized inside C70. By the same criterion, in the case of C60, only the endohedral complex with one H2 molecule is energetically stable. Our results are consistent with the fact that recently both (H 2)n@C70 (n = 1, 2) and H2@C 60 were prepared, but not (H2)3@C70 or (H2)2@C60. The ZPE of the coupled T-R motions, from the DMC calculations, grows rapidly with the number of caged p-H2 molecules and is a significant fraction of the well depth of the intermolecular PES, 11% in the case of p-H2@C70 and 52% for (p-H2)2@C70. Consequently, the T-R ZPE represents a major component of the energetics of the encapsulated H2 molecules. The inclusion of the ZPE nearly doubles the energy by which (p-H2)3@C70 is destabilized and increases by 66% the energetic destabilization of (p-H2)2@C 60. For these reasons, the T-R ZPE has to be calculated accurately and taken into account for reliable theoretical predictions regarding the stability of the endohedral fullerene complexes with hydrogen molecules and their maximum H2 content.

AB - Recent synthesis of the endohedral complexes of C70 and its open-cage derivative with one and two H2 molecules has opened the path for experimental and theoretical investigations of the unique dynamic, spectroscopic, and other properties of systems with multiple hydrogen molecules confined inside a nanoscale cavity. Here we report a rigorous theoretical study of the dynamics of the coupled translational and rotational motions of H 2 molecules in C70 and C60, which are highly quantum mechanical. Diffusion Monte Carlo (DMC) calculations were performed for up to three para-H2 (p-H2) molecules encapsulated in C70 and for one and two p-H2 molecules inside C 60. These calculations provide a quantitative description of the ground-state properties, energetics, and the translation-rotation (T-R) zero-point energies (ZPEs) of the nanoconfined p-H2 molecules and of the spatial distribution of two p-H2 molecules in the cavity of C70. The energy of the global minimum on the intermolecular potential energy surface (PES) is negative for one and two H2 molecules in C70 but has a high positive value when the third H2 is added, implying that at most two H2 molecules can be stabilized inside C70. By the same criterion, in the case of C60, only the endohedral complex with one H2 molecule is energetically stable. Our results are consistent with the fact that recently both (H 2)n@C70 (n = 1, 2) and H2@C 60 were prepared, but not (H2)3@C70 or (H2)2@C60. The ZPE of the coupled T-R motions, from the DMC calculations, grows rapidly with the number of caged p-H2 molecules and is a significant fraction of the well depth of the intermolecular PES, 11% in the case of p-H2@C70 and 52% for (p-H2)2@C70. Consequently, the T-R ZPE represents a major component of the energetics of the encapsulated H2 molecules. The inclusion of the ZPE nearly doubles the energy by which (p-H2)3@C70 is destabilized and increases by 66% the energetic destabilization of (p-H2)2@C 60. For these reasons, the T-R ZPE has to be calculated accurately and taken into account for reliable theoretical predictions regarding the stability of the endohedral fullerene complexes with hydrogen molecules and their maximum H2 content.

UR - http://www.scopus.com/inward/record.url?scp=77954641932&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=77954641932&partnerID=8YFLogxK

U2 - 10.1021/ja103062g

DO - 10.1021/ja103062g

M3 - Article

VL - 132

SP - 9826

EP - 9832

JO - Journal of the American Chemical Society

JF - Journal of the American Chemical Society

SN - 0002-7863

IS - 28

ER -