Microwave rotation-tunneling spectroscopy of the water–methanol dimer: Direct structural proof for the strongest bound conformation

Abstract

O between 7 and 24 GHz using a Fourier-transform microwave spectrometer. Because CH 3 OH and H 2 O are capable of both accepting and donating hydrogen bonds, there exists some question as to which donor-acceptor pairing of the molecules is the lowest energy form. This question is further emphasized by the ambiguity and variety present in previous experimental and computational results. Transitions arising from the methyl torsional A state were assigned in each of the studied isotopomers, and for the A and E states in , where the errors correspond to 1 uncertainties-are consistent with either conformation, the fit of the structure to the rotational constants demonstrates unambiguously that the lower-energy conformation formed in supersonically cooled molecular beams corresponds to a water-donor, methanol-acceptor complex. The results and implications for future work are also discussed in terms of the permutation-inversion theory presented by Hougen and Ohashi ͓J. Mol. Spectros. 159, 363 ͑1993͔͒.

Quantum Mechanical Study of the Nonbonded Forces in Water−Methanol Complexes

“…Using microwave spectroscopy for the water-methanol system, Suenram and co-workers determined an oxygen-oxygen distance of 2.997 ± 0.009 Å and a hydrogen bond angle of 179 ± 1°, which they attributed to the WdM configuration. 4 The theoretically determined distances and angles for either the MdW or WdM configuration are in poor agreement with these values, despite the rather high level of theory employed. The disagreements between the MP2/aug-cc-pVTZ geometry and the experimental geometry (Δ rO---O = 0.16 Å and Δθ H-bond = 13°) may arise from several sources.…”

Using the C–O stretch to unravel the nature of hydrogen bonding in low-temperature solid methanol–water condensates

“…Therefore, it would appear that the presence of H 2 O environment has little effect on the CH 3 OH PD hydrogen bonds. It has been reported in literature [33][34][35]39,58 that gas phase and matrix isolated heterodimers of CH 3 OH and H 2 O preferentially and exclusively bond with the CH 3 OH acting as a PA and the H 2 O as PD. Within an amorphous solid where a random arrangement of molecules and hydrogen bonded configurations are likely, it is still possible that during deposition there is preferential adsorption of CH 3 OH and H 2 O in the CH 3 OH(PA)· · · H 2 O(PD) arrangement.…”

“…In CH 3 OH the vibrational spectra of the O-H, C-H and the C-O stretch are sensitive to the interaction between nearest neighbours. The interactions between CH 3 OH and H 2 O have been studied in mixed CH 3 OH/H 2 O liquids [29][30][31][32] , heterodimers [33][34][35] and small clusters both in the gas phase and in matrix isolation studies 33,34 , supported with extensive computational studies [36][37][38][39][40][41][42][43][44] . The O-H stretch has been used extensively to study hydrogen bonding between H 2 O and CH 3 OH in dimers, matrix isolation and in clusters, however, in the bulk condensed and liquid phases this poses a problem as the broad absorption bands due to the O-H stretching frequencies of both CH 3 OH and H 2 O overlap.…”

Ab initio NMR study of the isomeric hydrogen‐bonded methanol–water complexes

“…OH 2 ). It was recently established that these two methanol-water complexes have equivalent binding energies [13][14][15], even in the liquid case [16].…”