Energetics and dynamics of H$_2$ adsorbed in a nanoporous material at low temperature

TL;DR

This study combines computational and experimental methods to analyze hydrogen adsorption energetics and dynamics in a nanoporous MOF-74, revealing detailed energy levels and confirming binding site characteristics.

Contribution

It provides a comprehensive computational analysis of H$_2$ binding sites, energy levels, and dynamics in MOF-74, validated by experimental neutron scattering data.

Findings

H$_2$ binding energy is approximately 100 meV after zero point energy correction.

Calculated rotational-translational energy levels agree with neutron scattering measurements.

Confirmed primary and secondary binding sites for H$_2$ in MOF-74.

Abstract

Molecular hydrogen adsorption in a nanoporous metal organic framework structure (MOF-74) was studied via van der Waals density-functional calculations. The primary and secondary binding sites for H$_2$ were confirmed. The low-lying rotational and translational energy levels were calculated, based on the orientation and position dependent potential energy surface at the two binding sites. A consistent picture is obtained between the calculated rotational-translational transitions for different H$_2$ loadings and those measured by inelastic neutron scattering exciting the singlet to triplet (para to ortho) transition in H$_2$. The H$_2$ binding energy after zero point energy correction due to the rotational and translational motions is predicted to be $\sim$100 meV in good agreement with the experimental value of $\sim$90 meV.