Nature of the bound states of molecular hydrogen in carbon nanohorns.

The effects of confining molecular hydrogen within carbon nanohorns are studied via high-resolution quasielastic and inelastic neutron spectroscopies. Both sets of data are remarkably different from those obtained in bulk samples in the liquid and crystalline states. At temperatures where bulk hydrogen is liquid, the spectra of the confined sample show an elastic component indicating a significant proportion of immobile molecules as well as distinctly narrower quasielastic line widths and a strong distortion of the line shape of the para-->ortho rotational transition. The results show that hydrogen interacts far more strongly with such carbonous structures than it does to carbon nanotubes, suggesting that nanohorns and related nanostructures may offer significantly better prospects as lightweight media for hydrogen storage applications.

Double-walled carbon nanotubes under hydrostatic pressure: Raman experiments and simulations.

We have used Raman spectroscopy to study the behavior of double-walled carbon nanotubes (DWNT) under hydrostatic pressure. We find that the rate of change of the tangential mode frequency with pressure is higher for the sample with traces of polymer compared to the pristine sample. We have performed classical molecular dynamics simulations to study the collapse of single (SWNT) and double-walled carbon nanotube bundles under hydrostatic pressure. The collapse pressure (pc) was found to vary as 1/R3, where R is the SWNT radius or the DWNT effective radius. The bundles showed approximately 30% hysteresis and the hexagonally close packed lattice was completely restored on decompression. The pc of a DWNT bundle was found to be close to the sum of its values for the inner and the outer tubes considered separately as SWNT bundles, demonstrating that the inner tube supports the outer tube and that the effective bending stiffness of DWNT, D(DWNT) - 2D(SWNT).