Prototropic charge migration in water. Part 1.—Rate constants in light and heavy water and in salt solution from oxygen-17 spin relaxation

Oxygen-17 scalar relaxation data from light and heavy water and from KCl solutions are reported. From the pH dependence of the relaxation, we extract the rate constants for proton transfer between H2O and H3O+(k+) and between H2O and OH–(k–). In H2O at 28 °C, we find k+=(7.1 ± 0.4)× 109 dm3 mol–1 s–1 and k–=(3.4 ± 0.2)× 10–9 dm3 mol–1 s–1. The kinetic H/D isotope effect is 1.6 ± 0.2 for k+ and 2.7 ± 0.4 for k–. The 1H—17O spin–spin coupling constant (JOH) in H2O, which is needed for the calculation of the rate constants, was redetermined, and we obtained JOH= 81.1 Hz, in good agreement with previous direct measurements but differing from the commonly adopted value.