Raman spectroscopic evidence for the most stable water/ethanol dimer and for the negative mixing energy in cold water/ethanol trimers

Abstract

Spontaneous Raman scattering in supersonic jet expansions is used to prove that the mixed dimer of ethanol and water (corresponding to a volume fraction of 79% ethanol in the liquid) prefers ethanol in a gauche conformation as the hydrogen bond acceptor. This represents a particularly simple case of adaptive aggregation. Furthermore, it is shown experimentally that the isolated cold trimer built from one ethanol and two waters (corresponding to 64% ethanol in the liquid) has a significantly negative excess enthalpy, in line with the thermodynamic bulk observation at room temperature.

Spectroscopic identification of ethanol-water conformers by large-amplitude hydrogen bond librational modes

“…A sensitive and well-established spectroscopic probe for hydrogen-bonded molecular complexes is the vibrational OHstretching manifold of the donor subunits 5,6 and a recent combined infrared and Raman investigation has monitored the donor OH-stretching spectral red-shifts for mixed 1:1 complexes of water with methanol and ethanol adiabatically cooled in supersonic jet expansions. 7,8 The vibrational assignments confirmed microwave molecular beam studies 9 that water acts as the hydrogen bond donor in the most stable conformations of both mixed alcohol/water complexes. 7 Based on the lower limit of the effective conformational temperature in the supersonic jet expansions of 10 K, the energy difference between the two most stable conformations of the mixed ethanol/water complex has been estimated to be higher than 0.2 kJ mol −1 from dedicated collisional relaxation experiments.…”

“…7 Based on the lower limit of the effective conformational temperature in the supersonic jet expansions of 10 K, the energy difference between the two most stable conformations of the mixed ethanol/water complex has been estimated to be higher than 0.2 kJ mol −1 from dedicated collisional relaxation experiments. 8 However, a recent microwave molecular beam work 9 has only identified the single conformation with ethanol as the hydrogen bond acceptor in the g + configuration and more experimental evidence has been welcomed to shed more light on this internal conformational isomerism issue.…”

Concentration‐Dependent Hydrogen‐Bonding Effects on the Dimethyl Sulfoxide Vibrational Structure in the Presence of Water, Methanol, and Ethanol

“…refs. [18][19][20][21][22][23][24]). To identify intermolecular interactions by using vibrational spectroscopy, changes in bond strength in terms of elongation or contraction are utilized as they are followed by changed dipole moments and can eventually manifest in the spectra as red-or blue-shifted vibrational frequencies, respectively.…”

Exploration of the (ethanol)4–water heteropentamers potential energy surface by simulated annealing and Ab initio molecular dynamics

“…T here is a growing interest in ethanol-water mixtures, both from experimental [1][2][3] and theoretical [4,5] points of view, because these are intermediates in the production of bioethanol by fermentation of agricultural products such as corn and sugarcane [6,7]. Bioethanol is one of the most relevant biofuels with excellent prospects for increasing its production and consumption worldwide since many countries have been implementing laws for its compulsory use because this is a renewable alternative fuel [8,9].…”