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

Abstract

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 (J_OH) in H₂O, which is needed for the calculation of the rate constants, was redetermined, and we obtained J_OH= 81.1 Hz, in good agreement with previous direct measurements but differing from the commonly adopted value.