On the Proton Affinity of Water

Ion–molecule reactions of proton transfer from H3O+ and to H2O were studied with several mixtures in a Bendix TOF mass spectrometer at pressures of 0.05–0.10 torr and in a CEC 21-110B mass spectrometer at pressures as high as 0.25 torr. Proton transfer was observed from H3O+ to C3H6, cis-2-C4H8, and CH2O; proton transfer was observed to H2O only from C2H5+, and not s-C3H7+ or s-C4H9+. These observations support the value of P.A. (H2O) = 164 ± 4 kcal/mole.