Neutron spectroscopy study of single-walled carbon nanotubes hydrogenated under high pressure

Single-walled carbon nanotubes (SWNT) were loaded with 5.2 wt% hydrogen at a hydrogen pressure of 3GPa and T = 620 K, quenched to 80K and studied at ambient pressure and 15K by inelastic neutron scattering (INS) in the range of energy transfers 3-400 meV. An analysis of the measured INS spectra showed that the quenched SWNT & H sample contained hydrogen in two different forms, as H atoms covalently bound to the carbon atoms (~4.7 wt%) and as H2 molecules (~0.5 wt%) exhibiting nearly free rotational behavior. Annealing the sample in vacuum at 332K removed about 65% of the H2 molecules and annealing at 623K removed all of them. This demonstrates that H2 molecules were kept in this sample more tightly than in earlier studied SWNT & H samples that were hydrogenated at lower pressures and temperatures and lost all molecular hydrogen on heating in vacuum to room temperature.