Dynamics of endoergic bimolecular proton transfer reactions: F-+ROH -> HF+RO- (R = H, CH3, CH3CH2, (CH3)(2)CH, and (CH3)(3)C)

Guided ion beam tandem mass spectrometry techniques are used to measure rea ction threshold energies for proton transfer of water, methanol, ethanol, 2 -propanol, and 2-methyl-2-propanol with fluoride anion, F- + ROH --> RO- HF, where R = H, CH3, CH3CH2, (CH3)(2)CH, or (CH3)(3)C. The measured reacti on threshold energy is an upper limit for the gas-phase acidity of the alco hol relative to hydrogen fluoride. Our guided ion beam measurements yield t hreshold energies that are consistently higher than those based on current literature pas-phase acidity values by 5-9 kJ/mol, indicating that the reac tions have a small effective barrier in excess of the endoergicity. To help interpret the experiments, ab initio and density functional theory techniq ues are used to calculate the proton transfer reaction potential energy sur faces. No intrinsic barriers Or double minima along the reaction path are f ound on the potential energy surfaces, Possible dynamical bottlenecks for t ranslational activation are discussed in detail.