Using a line shape simulation methodology that has been successfully applied to MOFs, we can distinguish between these two possibilities. From molecular dynamics (MD) simulations we extract the trajectories of the adsorbed CO2 molecules. We then calculate the residual chemical shift anisotropy (i.e. the chemical shift line width) based on these trajectories, following a previously published methodology that we implemented in a publicly available Python package. A similar, but slightly less efficient methodology was also published by Alavi et al. in 2008. Experimental Section