The vibrational and electronic properties of hydrogen molecules adsorbed on single-wall carbon nanotubes were investigated by high-resolution electron-energy-loss spectroscopy. We found that the adsorption of ${\mathrm{H}}_2$ molecules is dissociative at room temperature and $2.6\times {10}^{-2}\mathrm{Pa}.$ The C-H bond formed upon hydrogen adsorption has a vibrational energy equal to 360 meV, in agreement with the expected ${\mathrm{sp}}^2-{\mathrm{sp}}^3$ H-induced local rehybridization. The hydrogenation of carbon nanotubes also gives rise to significant changes for both the line shape and the excitation energy of the $\pi$ plasmon. Upon H adsorption, the plasmon shifts by 0.8 eV towards lower energies and, moreover, a weak feature rises up at 3.5 eV.

• Received 24 September 2003

DOI:https://doi.org/10.1103/PhysRevB.69.153409