Neutron diffraction (ND) measurements on liquid methanol (CD3OD,CD3O(H/D),CD3OH) under ambient conditions have been performed to obtain the total (intra-+intermolecular), Gdist(r) and intermolecular, Ginter(r) radial distribution functions (rdfs) for the three samples. The extent to which intermolecular structure is affected by using two different intramolecular models is discussed. The H/D substitution on hydroxyl–hydrogen (Ho) has been used to extract the partial distribution functions, GXHodist/inter(r) (X=C, O, and H—a methyl hydrogen) and GXXdist/inter(r) from the difference techniques of ND at both the distinct and intermolecular levels. The O–Ho bond length, which has been the subject of controversy in the past, is found purely from the partial distribution function, GXHodist(r) to be 0.98±0.01 Å. The C–H distance obtained from the GXXdist(r) partial is 1.08±0.01 Å. These distances determined by fitting an intramolecular model to the total distinct structure functions are 0.961±0.001 Å and 1.096±0.001 Å, respectively. The GXXinter(r) function, dominated by contributions from the methyl groups, apart from showing broad oscillations extending up to ∼14 Å is featureless, mainly because of cancellation effects from six contributing pairs. The Ho⋯Ho partial pair distribution function (pdf), gHoHo(r), also determined from the second-order difference, shows that only one other Ho atom can be found within a mean Ho⋯Ho separation of 2.36 Å. The average position of the O⋯Ho hydrogen bond determined purely from experimental GXHointer(r) partial distribution function, at 1.75±0.03 Å is found to lie in the range (1.75–1.95 Å) of values reported from computer simulation results.

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Molecular dynamics (MD) simulations of pure methanol (216 molecules) have been carried out at 298.15 K in the NVE ensemble using a six-site potential model originally derived by Anwander et al (1992 Chem. Phys. 166 341) from ab initio quantum chemical calculations (QCC) and tested for the first time in this study. MD results of a three-site model where all the methyl hydrogens were considered as a dead load have also been reported recently by us. In this paper, the relative merits of the two models are discussed by comparing the simulated radial distribution functions (rdfs) with the recent experimental neutron diffraction (ND) results obtained at the partial pair distribution function (pdf) level. Although the MD simulations with both the models reproduce the total rdfs rather well, discrepancies begin to appear at the partial pdf level. Both the simulations are found to reproduce equally well the X-X (X = C, O or H, a methyl hydrogen) pdf since it comprises six correlations, and is dominated mainly by contributions from the methyl group. However, the main peaks of the simulated HO-HO partial, where HO is the hydroxyl hydrogen, are found to be slightly higher and shifted to larger distances as compared to the ND results. A comparison of the simulated X-HO intermolecular rdf, in which H-HO correlations dominate, with the ND results shows that, although the three-site model reproduces at least qualitatively the experimental features, the six-site model derived from ab initio QCC fails badly.