Noncoincidence effect in the C-O and O-H stretching modes of methanol: a polarized Raman and DFT study

In this study, the optimal geometry and vibrational properties of methanol were analysed bythe density functional theory (DFT) approach and polarized Raman spectroscopy. Global minimumstructures of methanol molecular clusters were generated using ABCluster software.DFT and frontier molecular orbital (FMO) were applied to structurally and thermodynamicallyinvestigate various methanol molecular clusters. Using these methods, the intermolecular interactionpotential energies and HOMO-LUMO gap energies of methanol dimer, trimer, and tetramerclusters were calculated. As a result, dimer-helical, cyclic trimer-uud, and cyclic tetramer-udud clusters with the highest structural and thermodynamic stability of methanol wereidentified. Experimental and computational methods were used to determine the isotropic andanisotropic components of the methanol C-O and O-H spectral bands. The data obtainedshowed that an anisotropic component cannot form in the dimer cluster. The characteristics ofthe polarized Raman spectrum of the cyclic tetramer cluster were found to be similar to the experimentalresults.