  The ionization constant of water Kw is currently determined on the proton
conductivity sigma1 which is measured at frequencies lower than 10^7 Hz. Here,
we develop the idea that the high frequency conductivity sigma2 (~10^11 Hz),
rather than sigma1 represents a net proton dynamics in water, to evaluate the
actual concentration c of H3O+ and OH- ions from sigma2. We find c to be not
dependent on temperature to conclude that i) water electrodynamics is due to a
proton exchange between H3O+ (or OH-) ions and neutral H2O molecules rather
than spontaneous ionization of H2O molecules, ii) the common Kw (or pH)
reflects the thermoactivation of the H3O+ and OH- ions from the potential of
their interaction, iii) the lifetime of a target water molecule does not exceed
parts of nanosecond.

Chemical Physics