Dissociation Energies of Some Gaseous Alkali Halide Complex Ions and the Hydrated Ion K(H2O)+

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Abstract
A mass spectrometer was used to analyze the ionic species present in the vapors of several alkali halides which were heated in a small oven to temperatures in the range 700–950°K. For the four compounds investigated, NaCl, KCl, KBr, and RbCl, the most abundant ionic species were of the type M+ and M2X+ in comparable amounts. Smaller amounts of M3X2+ ions and, in certain circumstances, negative ions of the type X— and MX2— were also detected. The equilibrium constant was measured as a function of temperature for the reaction M2X(g)+→M(g)++MX(g). Values of the ΔH of this reaction were determined by two independent methods which gave good agreement for all compounds except RbCl. The values of ΔH(0°K) so determined were 42.3, 41.3, and 41.0 kcal/mole for NaCl, KCl, and KBr, respectively. The more reliable value for RbCl was about 40 kcal/mole which agrees well with a theoretically calculated value of about 42 kcal/mole. An attempt to detect the K(H2O)+ ion in equilibrium with water vapor and KCl at about 840°K was apparently successful, although positive identification of the ion could not be made. The equilibrium constant for the reaction K(H2O)(g)+→K(g)++H2O(g) was measured and gave a value of ΔH(O°K) = 20 kcal/mole.

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