  We have studied molecular hydrogen in a pure 1D geometry and inside a narrow
carbon nanotube by means of the diffusion Monte Carlo method. The
one-dimensionality of H2 in the nanotube is well maintained in a large density
range, this system being closer to an ideal 1D fluid than liquid 4He in the
same setup. H2 shares with 4He the existence of a stable liquid phase and a
quasi-continuous liquid-solid transition at very high linear densities.
