Spectroscopy of a rotating hydrogen molecule in carbon nanotubes

International audienceA first-principles study of the spectroscopy of a single hydrogen molecule rotating inside and outside ofcarbon nanotubes is presented. Density functional theory (DFT)-based symmetry-adapted perturbationtheory (SAPT) is applied to analyze the influence of the rotation in the dispersionless and dispersionenergy contributions to the adsorbate–nanotube interaction. A potential model for the H2–nanotubeinteraction is proposed and applied to derive the molecular energy levels of the rotating hydrogenmolecule. The SAPT-based analysis shows that a subtle balance between the dispersionless anddispersion contributions is key in determining the angular dependence of the H2–nanotube interaction,which is strongly influenced by the diameter of the carbon nanotubes. As a consequence, the structureof molecular energy levels is very different in wide and narrow nanotubes with the diameter aboveand below 1 nanometer, respectively. Strong anisotropy effects lead to a rather constrained rotation ofmolecular hydrogen inside narrow nanotubes