Structural transformations in bulk and matrix-isolated methanol from measured and computed infrared spectroscopy

FTIR spectra of methanol trapped in an Ar matrix were registered during gradual heating of the sample. The spectral changes observed in these experiments indicate a transformation from isolated methanol monomers to small hydrogen-bonded clusters, allowing us to consider such experiments as an experimental model of the gas–liquid phase transition. The liquid–solid phase transition for methanol was investigated by analysing the temperature dependence of the registered FTIR spectra of methanol during cooling from −70°C to −115°C. Comparing the experimental spectra in the CO stretching region with results of quantum-chemical calculations using the method of principal component analysis we draw conclusions about the size and structure of the methanol clusters formed in the sample at different temperatures. •Temperature evolution of FTIR spectra of methanol•Quantum-chemical calculations of 17 different methanol clusters•Dominating cluster structures for different methanol phases were determined.