The water-solvated methanol ion and its isomers: experiment and theory

Tandem mass spectrometry combined with ab initio calculations was used to explore the chemistry of the water-solvated methanol cation and its isomers, including the distonic methanol ion solvated by water, ⋅CH2OH2+/H2O (I), the methanol molecular ion associated with water, CH3OH⋅+/H2O (II), and protonated methanol bound with a hydroxyl radical, CH3OH2+/HO⋅ (IV). Another ion, [<F>H2O⋯H&z.sbnd;CH2OH⋅+</F>] (III), where the water molecule is attached to a methyl H of the methanol cation, proved inaccessible experimentally although it was predicted to be stable in a shallow potential well by theoretical calculations. The ions were generated by collision-induced loss of a radical or atom from appropriate proton bound molecular pairs. The heats of formation of ions (I) to (IV) were calculated to be 448, 482, 486 and 538 kJ/mol, respectively. Ions (I), (II) and (IV) can be identified by their metastable ion and collision-induced dissociation mass spectra. A partial potential energy surface linking the isomers is used to discuss the experimental data obtained with deuterium-labeled species. [Copyright &y& Elsevier]