Spectroscopy of a rotating hydrogen molecule in carbon nanotubes

Authors: Pilar de Lara-Castells, Maria; Mitrushchenkov, Alexander O.

Contribution: Article

Journal: PHYSICAL CHEMISTRY CHEMICAL PHYSICS

Publication date: 2019/02/21

DOI: 10.1039/c8cp04109a

Abstract: A first-principles study of the spectroscopy of a single hydrogen molecule rotating inside and outside of carbon nanotubes is presented. Density functional theory (DFT)-based symmetry-adapted perturbation theory (SAPT) is applied to analyze the influence of the rotation in the dispersionless and dispersion energy contributions to the adsorbate-nanotube interaction. A potential model for the H-2-nanotube interaction is proposed and applied to derive the molecular energy levels of the rotating hydrogen molecule. The SAPT-based analysis shows that a subtle balance between the dispersionless and dispersion contributions is key in determining the angular dependence of the H-2-nanotube interaction, which is strongly influenced by the diameter of the carbon nanotubes. As a consequence, the structure of molecular energy levels is very different in wide and narrow nanotubes with the diameter above and below 1 nanometer, respectively. Strong anisotropy effects lead to a rather constrained rotation of molecular hydrogen inside narrow nanotubes.