The heats of formation of some C₂H₅O⁺ isomers, relevant bond energies in ethanol and PA(CH₃CHO)

The ionization potentials of the transient species CH₃CH₂O, CH₃CHOH, and CH₂CH₂OH (generated by the F+ethanol reactions) are measured by photoionization mass spectrometry: I.P.(CD₃CD₂O)=10.29±0.08 eV (tentative), I.P.(CH₃CHOH)<6.85 eV, and I.P.(CD₂CH₂OH) ≤8.35±0.06 eV. The latter results in a cation of uncertain structure. These reactions also generate vinyl alcohol (adiabatic I.P.=9.33±0.01 eV) and acetaldehyde. A redetermined appearance potential of CH₃CHOH⁺ from ethanol enables one to infer the proton affinity of acetaldehyde to be ≥183.8±0.2 kcal/mol and an α (C–H) bond energy in ethanol ≳91.1 kcal/mol (0 K). The appearance potential of m/e=45 ion from bromoethanol is interpreted as formation of a C₂H₅O⁺ isomer having the oxirane structure, with ΔH_f0⁰ of ∼173.9 kcal/mol, consistent with earlier alternative measurements. A second increase in the m/e=45 ion yield curve from ethanol is interpreted as formation of this same isomer. This interpretation, and an alternative cycle, lead to a β (C–H) bond energy in ethanol of 98±2 kcal/mol. The implication of the current results to the dynamics of dissociation of ethanol cations is discussed.