  A theoretical study on the rotational dynamics of H2 molecules trapped in the
interstitial channels (ICs) of a carbon nanotube bundle is presented. The
potential used in this study is modeled as a sum of atom-atom (C-H) van der
Waals interactions and electrostatic interactions of the molecule with the
surrounding nanotubes.The rotational energy spectra is calculated using a
product wave function, where the coupling between translational and rotational
modes is treated in a mean-field manner . Molecular dynamics (MD) simulation
study was performed for estimating the hydrogen rotational barrier. Both
theoretical calculations and simulation results reveal the existence of a large
rotational barrier (~ 40 meV). The consequences of this rotational barrier for
the rotational energy levels are worked out in detail.
