Equivalence of hydrogen and deuterium bonds in methanol: mixed cyclic clusters from cross-aggregation revealed by matrix isolation IR, DFT, and NCI/RDG analyses.

This study investigates the temperature-driven structural evolution and intermolecular interactions of deuterated methanol clusters, employing argon matrix isolation infrared (IR) spectroscopy combined with density functional theory (DFT) calculations. A central comparison is made between hydrogen bonds (O-H⋯O) and deuterium bonds (O-D⋯O) in methanol and its deuterated isotopologues. Both DFT calculations and non-covalent interaction (NCI)/reduced density gradient (RDG) analyses reveal that hydrogen and deuterium bonds are nearly identical in strength. Consequently, in mixtures of normal methanol and deuterated methanol (CH3OD or CD3OD), the cyclic clusters formed upon annealing are not phase-separated but rather consist of mixed hydrogen/deuterium-bonded rings. Matrix isolation experiments show that the area ratio SOH/SOD undergoes a characteristic change with temperature: as aggregation increases, the proportion of deuterium bonds first rises and then falls. Furthermore, deuteration of the methyl group (CD3OD) enhances the stability of deuterium bonds, leading to a higher relative proportion in mixed aggregates. This work provides molecular-level evidence for the equivalence of hydrogen and deuterium bonds in driving aggregation and offers a refined view of isotope effects in hydrogen-bonded networks.