Equivalence of hydrogen and deuterium bonds in methanol: mixed cyclic clusters from cross-aggregation revealed by...

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 S_OH/S_OD 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.