A Density Functional Study of Methanol Clusters

Abstract

The potential energy surfaces of methanol clusters, (CH3OH)n, n = 2-12, have been studied using density functional theory at the B3LYP/6-31G(d) and higher levels of theory. Cyclic clusters in which n methanol molecules are joined in a ring structure formed by n hydrogen bonds are shown to be more stable than structures of the same number of methanol molecules where one or more methanol molecules are outside the ring and are hydrogen-bonded to oxygens of methanols in rings of n - 1, n - 2, and so forth. So-called chain structures are generally even less stable. Furthermore, the hydrogen-bonding energy per methanol molecule of the n-ring clusters is shown to converge to an asymptotic value of about 27 kJ/mol at B3LYP/6-311+G(d,p)//B3LYP/6-31G(d) after five to six methanols are included in the cluster. As expected, there are many minima on the potential energy surfaces of the methanol clusters, the number increasing rapidly with n. A cyclic cluster of five to six methanol molecules appears to be sufficient to mimic liquid behavior as far as vibrational frequencies are concerned.

Geometries and energetics of methanol–ethanol clusters: a VUV laser/time-of-flight mass spectrometry and density functional theory study

“…The hybrid density functional B3LYP (14) was used, since it has been shown to provide reliable results for hydrogen-bonded systems, including neat-alcohol clusters (15,16). Since an accurate de- scription of H-bonds requires a highly flexible basis set, the 6-311++G(d, p) basis set was used for geometry optimization, followed by single-point energy (SPE) calculations using a larger basis set, 6-311++G(3df, 2p).…”

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

“…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.…”

Infrared Absorption Spectra of Monohydric Alcohols

“…However the mechanism of the diffuse band formation and its structure are still the unsolved problems. e importance of the problems connected with the alcohol clustering and structure and, in particular, with the mechanisms of the diffuse absorption band formation is re�ected in the great number of experimental [1][2][3][4][5][6][7][8][9], theoretical [10][11][12][13][14], and combined works [15][16][17][18][19] published in the recent years.…”