Inelastic Neutron Scattering of H$_{2}$ Adsorbed on Boron Doped ($\sim $ 1\%) Single Walled Carbon Nanotubes

It is clear from this study that H$_{2}$ is preferentially adsorbed at boron sites in SWNTs and in these sites the H$_{2}$ experiences an orientational component in the potential. Thus, this study shows that the substitution of boron for carbon in the SWNT lattice produces higher energy binding sites for H$_{2}$ adsorption. We report here an inelastic neutron scattering investigation of H$_{2}$ adsorbed on $\sim $ 200 mg of purified boron doped ($\le $ 1{\%}) SWNT bundles. At H$_{2}$ coverages $\le $ 1 H$_{2}$/ B and at T = 3K, a clear splitting of $\sim $ 1.4 meV is observed for the sublevels of the J=1 state. As the H$_{2}$ coverage is increased, the rotational spectrum converges to that of the bulk like rotor observed for H$_{2}$adsorbed on undoped SWNTs with the appearance of a peak at 14.7 meV. As the temperature is increased from 3K, the bulk like peak decreases in intensity until only the split rotational peaks are present; the intensity of these peaks decreases with increasing temperature until about 75 K at which point no rotational peak is observable. Funding provided by the US DOE Office of Energy Efficiency and Renewable Energy within the Center of Excellence on Carbon-based Hydrogen Storage Materials.