Effect of Pressure on Hydrogen Bonding in Liquid Methanol

Abstract

We have investigated the effect of pressure on the hydrogen bonding in liquid methanol using Raman spectroscopy. Specifically, we have measured the OH and CO stretching modes and assigned the bands, in agreement with recent IR and crossed molecular beam experiments on methanol clusters. At about 7 to 8 kbar, we note indications that the intrinsic nature of the methanol clusters in our samples has changed. Our results provide support for and extend conclusions derived from Monte Carlo simulations, explain anomalies observed by previous researchers, and provide new insights into general hydrogen-bonding phenomena.

Are polar liquids less simple?

“…Some experiments [16,17,18,19,20] and mds [21,22] have shown that pressure increases H-bonding in non-aqueous liquids, while other studies have found that in alcohols, pressure either weakens hydrogen bonds [7,23] or has no effect [24].…”

Local Hydration Pressures in Methanol Aqueous Solution: A Raman Spectroscopy Analysis

“…A good agreement is found with the previous results of ref 20, except in the methanol-rich region, very likely due to the different numerical treatment of the signal in this complex feature of the Raman spectrum of methanol. 13 The changes observed in the CO-stretch region reveal a strong hydrogen-bonding interaction between methanol and water molecules. This behavior of methanol in aqueous solution is in clear contrast with that observed in pure liquid methanol under hydrostatic pressure.…”

“…13 The results are plotted in Figure 6, where it can be noticed that the addition of water leads to tensile pressures on the CO bond up to 4.5 GPa in the limit of x H 2 O = 1. It should be noted that this is an effective pressure, and it should be only considered like a relative measure of the attractive (hydrophilic) interaction on the COH group as a whole, in comparison with the repulsive (hydrophobic) interaction on the methyl group.…”

“…13,29 Such changes clearly reflect the effect on the hydrogen bonding interactions in the mixture, and deserve further analysis in order to express the frequency changes observed in terms of local pressures/stress exerted by the surrounding water molecules on the bonds of individual methanol molecules.…”

Diamond as pressure sensor in high‐pressure Raman spectroscopy using sapphire and other gem anvil cells

“…Raman spectroscopy is surely one of the most suitable techniques to follow pressure-induced phase transitions and to study other subsequent phenomena. According to the present results and other recent studies, 27 the tandem SAC-diamond pressure scale is recommended to carry out Raman experiments at moderate high pressures. This conclusion has special significance for Raman studies focused on polymers and biomaterials.…”