First-principles approach to rotational-vibrational frequencies and infrared intensity for H2 adsorbed in nanoporous materials

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 parahydrogen.