  The absorption sites and the low-lying rotational and vibrational (RV) energy
states for H$_2$ adsorbed within a metal-organic framework are calculated via
van der Waals density functional theory. The induced dipole due to bond
stretching is found to be accurately given by a first-principles driven
approximation using maximally-localized-Wannier-function analysis. The
strengths and positions of lines in the complex spectra of RV transitions are
in reasonable agreement with experiment, and in particular explain the
experimentally mysteriously missing primary line for para hydrogen.
