This paper is dedicated to Professor Camille Sandor-or1 the occc~sion of his 65th birtlzdayG. CALDWELL and P. KEBARLE. Can. J. Chem. 63, 1399Chem. 63, (1985.Experimental measurements of the gas phase ion equilibria X + HX = XHX-, X-(HX),,, + HX = X-(HX),,, and X-+ HY = XHY where X, Y = C1, Br. I, with a high pressure mass spectrometer, combined with the recent determination of F-+ HF = FHF-by Larson and McMahon, provide a very complete set of hydrogen bond dissociation enthalpies and free energies for the hydrogen bihalide ions. The bond energy trends In the different XHX-and X H Y are discussed. The data can be used also for the evaluation of lattice energies of salts containing the bihalide ions and for determinations of the solvation energies of these ions. [Traduit par le journal]