Publication: A spectroscopic and computer simulation study of butanol vapors

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Title A spectroscopic and computer simulation study of butanol vapors
Authors/Editors* G. S. Fanourgakis, Y. J. Shi, S. Consta, and R. H. Lipson
Where published* Journal of Chemical Physics
How published* Journal
Year* 2003
Volume 119
Number 13
Pages 6597-6608
Keywords cluster distribution, H-bonded clusters, grand canonical Monte Carlo
Clusters of butanol formed above neat liquid samples were entrained in a supersonic jet and probed using 10.5 eV vacuum ultraviolet laser single-photon ionization/time-of-flight mass spectrometry. The four different isomers of butanol ͑n-butanol, sec-butanol, iso-butanol, and tert-butanol͒ were studied separately to assess the influence of the structure of the alkyl chain on the formation and stability of the hydrogen bonded clusters. Most of the higher mass features observed in the mass spectra could be assigned to protonated alcohol clusters,that arise from facile proton-alkoxy radical/alkoxide anion dissociation. Signals due to protonated trimers were only evident in the spectra of tert- and sec-butanol. Empirical force fields, density functional theory and ab initio methods were used to identify the geometries of all clusters up to the pentamers for the different isomers. Monte Carlo simulations established vapor-phase cluster distributions, while molecular dynamics was used to assess the relative stability of the isomeric tetramers. Together, these experimental and theoretical results suggest that butanol tetramers are ‘‘magic-number’’ structures, and that the protonated ion signals of size n could be correlated with the neutral cluster of size n+1, provided the vapor pressures sampled in the supersonic jet exceeded equilibrium values.
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