Measurement of the hydration numbers for halogen ions by the mass spectrometric method of field evaporation of ions out of solution

The most probable hydration numbers, nmax, for halogen ions in liquid solutions have been determined by the mass spectrometric method of field evaporation of ions out of solution (FEIS): 2.5 (F−), 2.0 (Cl−), 1.5 (Br−), 1.0 (I−). The values of nmax are similar to the hydration numbers determined by other methods based on the measurement of ion mobilities and are half as large as nmax for the hydration of the same ions in water vapour. FEIS is the most direct and reliable method for studying the ion hydration in solutions.