Mechanisms of Sequential Ion-Molecule Reactions in Protonated Methanol using Mass Spectrometry, ab initio Methods, and Statistical Modeling

Joshua J. Melko

University of North Florida

Reactions of protonated methanol clusters, (CH₃OH)_nH⁺, are studied with mass spectrometry and computational chemistry. We find that the reaction of the protonated monomer with neutral methanol consists of two entrance complexes that are in equilibrium due to a very small barrier between them. Statistical modeling indicates that competition between proton transfer, condensation, and association are dictated by the depth of the proton-bound complex and the height of the S_N2 transition state. For the reaction of the protonated dimer we determine condensation is not energetically favorable at thermal energies as a solvation effect raises the S_N2 barrier. Geometries for protonated methanol clusters (CH₃OH)_nH⁺ up to n = 6 are also discussed, allowing for an examination of the role of entropy and hydrogen bonding in these structures.