  We study the low temperature phase behavior of hydrogen within a bundle of
carbon nanotubes. Because the carbon environment weakens the attraction between
molecules within the same interstitial channel (IC), the ground state of the
one-dimensional (1D) system is an uncondensed gas. When the screened attractive
interaction between molecules in adjacent ICs is taken into account, the
hydrogen ground state is a quasi-1D liquid. The critical temperature of this
system is estimated.
