Investigation of IR and Raman spectra of species present in formaldehyde-water-methanol systems

Formaldehyde forms a variety of hydrated and methoxylated species when reacted with water and methanol. Vibrational spectroscopy has been deployed for both remote and in situ sensing of formaldehyde species and it can be a useful tool for process development, monitoring and control at both laboratory and industrial scale, as well as for environmental, atmospheric and space monitoring. While IR and Raman spectroscopic studies of formaldehyde species in solid, liquid or gas phases have been reported, assignments of vibrational frequencies of relevant species in previous literature have been contradictory and incomplete. In this work we report IR and Raman spectra for formaldehyde-water-methanol solutions across a wide range of formaldehyde concentrations and solvent compositions. We present an analysis of vibrational spectra of formaldehyde-water-methanol systems using a combination of experimental measurements and gas phase quantum mechanical density functional theory simulations. For the first time, we explicitly consider spectra of oligomeric mixtures of formaldehyde species in relation to spectra of specific representative hydrated and methoxylated species and we resolve some previously reported contradictions in assignments of vibrational frequencies for formaldehyde systems.