The hydrates H+(H20), were observed in irradiated water vapor at pressures from 0.1 to 6 torr and temperatures from 15 to 600". Determination of the relative concentrations of the hydrates after mass analysis of the ions allows determination of the equilibrium constants Kn-l,,, for the reactions H+(HzO),,-l + HzO H+-(HzO),,. Determination of the equilibrium constants over the experimental range leads to values for AH,,-l,,,, AGon-l,,, and ASon-1.,,. The experimental values for -AH,+l,,,, and -AG",,--l,, in brackets, are: (1,2) 36 [ 2 5 ] ; (2,3) 22.3 [13.6]; (3,4) 17 [8.5]; ( 4 3 15.3 E5.51; (5,6) 13 E3.91; (6,7) 11.7 E2.81; (7,8) 10.3 E2.21 kcal/mole.The free-energy data are for 300°K and standard state of 1 atm. From these data one can calculate the hydrate distribution over a wide range of pressures and temperatures. It is shown that the AH and AS values are of reasonable magnitude. The continuous decrease of the AHndl,,, and AG,,-l,,, values shows that the stabilities of the hydrates H+(H20), change quite continuously. No single structure shows dominant stability. Comparison of the data with the proton affinity of water suggests that in the lower hydrates (n = 2 to 4 or even 6) all water molecules are equivalent. This would make the notation H30+(Hz0), inappropriate. The data also indicate that beyond n = 4 either a new "shell" is started or crowding of the first "shell" occurs. he interaction of ions with solvent molecules has -__ (8) J. G . Collins and P. Kebarle, J . Chem. Phys., 46, 1082 (1967).
