Weak intermolecular interactions in gas-phase NMR

TL;DR

This paper investigates how weak intermolecular forces influence NMR shielding constants in gas-phase systems, combining experimental NMR spectra with ab initio calculations to understand these subtle effects.

Contribution

It provides a detailed analysis of weak intermolecular interactions in gas-phase NMR and improves the accuracy of theoretical predictions by refining bulk susceptibility corrections.

Findings

Weak intermolecular forces affect NMR shielding constants.

Best agreement achieved with specific bulk susceptibility corrections.

Analysis of He-rare gas interactions enhances correction accuracy.

Abstract

Gas-phase NMR spectra demonstrating the effect of weak intermolecular forces on the NMR shielding constants of the interacting species are reported. We analyse the interaction of the molecular hydrogen isotopomers with He, Ne, and Ar, and the interaction in the He-CO_2 dimer. The same effects are studied for all these systems in the ab initio calculations. The comparison of the experimental and computed shielding constants is shown to depend strongly on the treatment of the bulk susceptibility effects, which determine in practice the pressure dependence of the experimental values. Best agreement of the results is obtained when the bulk susceptibility correction in rare gas solvents is evaluated from the analysis of the He-rare gas interactions, and when the shielding of deuterium in D_2-rare gas systems is considered.