First-principles approach to rotational-vibrational frequencies and infrared intensity for H$_2$ adsorbed in nanoporous materials

TL;DR

This paper uses first-principles calculations to determine the rotational-vibrational energy levels and infrared spectra of hydrogen molecules adsorbed in nanoporous materials, explaining experimental spectral features.

Contribution

It introduces a first-principles method to accurately predict RV frequencies and IR intensities for H₂ in metal-organic frameworks, including the missing primary line for para hydrogen.

Findings

Calculated RV energy states match experimental spectra.

Accurate prediction of IR line positions and intensities.

Explanation of the missing primary line for para hydrogen.

Abstract

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.