In order to highlight the importance of the PES structure (including inter-molecular anharmonicity) on glassy dynamics, the FTIR absorption data, specifically the OH vibrational stretch absorption for sorbitol, will be used as an illustrative example of the proposed hypothesis. Analysis of the FTIR data also reveals that the glass-transition temperatures are fundamental characteristics of the PES (rather than an exclusive low-frequency relaxation that couples to higher-frequency phenomena) since the OH stretching vibration has a cycle time of ≈ 60 fs, which is 11-20 orders of magnitude higher than the characteristic time of the αrelaxation motion. Since the strengths of covalent OH-bonds are highly influenced by their inter-molecular interactions (i.e. hydrogen bonds), the OH-stretch absorption characteristics can provide a measure of the inter-molecular interactions in the solid, an important component since traditional structural analyses (e.g. Xray diffraction) are not easily applied to disordered media and precise inter-molecular information is difficult to extract.