Encapsulation of a Water Molecule inside C60 Fullerene: The Impact of Confinement on Quantum Features

Orlando Carrillo-Bohórquez,Rita Prosmiti,Álvaro Valdés

doi:10.1021/acs.jctc.1c00662

Abstract

We introduce an efficient quantum fully coupled computational scheme within the multiconfiguration time-dependent Hartree (MCTDH) approach to handle the otherwise extremely costly computations of translational–rotational–vibrational states and energies of light-molecule endofullenes. Quantum calculations on energy levels are reported for a water molecule inside C60 fullerene by means of such a systematic approach that includes all nine degrees of freedom of H2O@C60 and does not consider restrictions above them. The potential energy operator is represented as a sum of natural potentials employing the n-mode expansion, along with the exact kinetic energy operator, by introducing a set of Radau internal coordinates for the H2O molecule. On the basis of the present rigorous computations, various aspects of the quantized intermolecular dynamics upon confinement of H2O@C60 are discussed, such as the rotational energy level splitting and the significant frequency shifts of the encapsulated water molecule vibrations. The impact of water encapsulation on quantum features is explored, and insights into the nature of the underlying forces are provided, highlighting the importance of a reliable first-principles description of the guest–host interactions.

Highlights

Compounds in which atoms or small molecules are trapped in the cavity of fullerenes, such as C60 or C70, are known as endofullerenes or endohedral fullerenes and offer the opportunity to explore unusual patterns of the entrapped species
A step advance in endofullerene science has been made with the advent of a novel, multistep organic synthesis procedure known as molecular surgery.[9−12,29,32−34] Such a procedure consists of a series of chemical reactions for creating an open C60 cage, in which the guest molecule can be inserted, followed by the closing of the cage with the guest trapped inside
Various molecules, such as H2, HD, HF, H2O, and CH4, have been encapsulated into C60 in this manner to date, and their properties have been experimentally investigated by X-ray diffraction, inelastic neutron scattering (INS), far-infrared spectroscopy (FIR), and nuclear magnetic resonance (NMR) spectroscopy techniques.[14,16−18] Such confined light molecules exhibit dominant quantum effects as a result of strong couplings between translational and rotational motions

Summary

INTRODUCTION

Compounds in which atoms or small molecules are trapped in the cavity of fullerenes, such as C60 or C70, are known as endofullerenes or endohedral fullerenes and offer the opportunity to explore unusual patterns of the entrapped species. A step advance in endofullerene science has been made with the advent of a novel, multistep organic synthesis procedure known as molecular surgery.[9−12,29,32−34] Such a procedure consists of a series of chemical reactions for creating an open C60 cage, in which the guest molecule can be inserted, followed by the closing of the cage with the guest trapped inside Various molecules, such as H2, HD, HF, H2O, and CH4, have been encapsulated into C60 in this manner to date, and their properties have been experimentally investigated by X-ray diffraction, inelastic neutron scattering (INS), far-infrared spectroscopy (FIR), and nuclear magnetic resonance (NMR) spectroscopy techniques.[14,16−18] Such confined light molecules exhibit dominant quantum effects as a result of strong couplings between translational and rotational motions.

COMPUTATIONAL DETAILS

RESULTS AND DISCUSSION

Energies of 9D MCTDH

SUMMARY AND CONCLUSIONS

■ ACKNOWLEDGMENTS

■ REFERENCES