Structure and vibrational spectra of methanol clusters from a new potential model

Abstract

The structures and vibrational spectra of small methanol clusters from dimer to decamer have been calculated using a newly developed intermolecular potential which is essentially based on monomer wave functions. Special care has been taken for the description of the electrostatic interaction using a distributed multipole representation and including a penetration term. In addition, the potential model consists of repulsion, dispersion, and induction terms. Based on this potential model cluster structures have been calculated. The lowest energy dimer configuration is linear, while from trimer to decamer for the most stable structures ring configurations were found. Tetramer, hexamer, and octamer have S4-, S6-, and S8-symmetry, respectively. Vibrational spectra of the CO stretch and the OH stretch mode have been determined in the harmonic and in the anharmonic approximation using perturbation theory and variational calculations. Up to the tetramer the experimental spectra of the CO stretch mode are well reproduced, for larger clusters an increasing blueshift with respect to the experimental evidence is found. The experimental data for the OH stretch mode of the dimer are fairly well reproduced in all approximations, however, the spectrum of the trimer can only be reproduced using the variational calculation which includes Darling–Dennison resonance terms.

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

“…Therefore, the large energy gain due to the formation of the tetramers should be associated with its abundance in the vapor, along with the supersaturation effect discussed before. A similar energy trend has been reported for neat methanol and water vapors (1,2). It should be noted that methanol prefers to form larger clusters than water (1).…”

“…and [2] suggest that the probability of protonated (N -1)-mer formation can be correlated to the abundance of the neutral N-mer. Such a correlation would be invalid for van der Waals clusters because, upon ionization, they lose monomer units uncontrollably by evaporation (10).…”

“…Thus, the combination of evaporative cooling due to the loss of one ligand (eqs. [1] and [2]) and solvated proton-ligand polarization makes further ligand loss difficult. Although this effect will become less important with increasing neutral-cluster size, the ion intensities recorded by VUV laser/mass spectrometry should qualitatively correlate with the neutral-cluster distribution in the supersonic expansion.…”

“…For small alcohol clusters such as methanol (Me) or ethanol (Et), H-bonds play a key role in determining the most-stable structures (4), whereas the alkyl chains have a more pronounced effect in larger clusters, as shown in our earlier studies of butanols (5). Despite the extensive amount of research that has been done on neat alcohols (1)(2)(3), the number of studies on alcohol mixtures, specifically on their vapor cluster compositions, is quite limited. In this work, VUV laser/time-of-flight (TOF) mass spectrometry was used to probe Me-Et clusters formed in the vapor phase above their liquid mixtures.…”

Facile isolation of a stable S6-symmetric methanol hexamer using the guest-free microporous metal-organic framework: zinc 5-tert-butyl isophthalate

“…Information on many methanol oligomers has been obtained by a variety of spectroscopic methods [12,14], but crystallography yields more definitive information if the oligomers can be isolated in the solid state [15][16][17]. This has been achieved in some cases by isolating methanol oligomers during the crystallization of various materials [15,16], including porous MOFs [18,19], or by solvent exchanging [20,21], or adsorbing [11] methanol into porous materials.…”