The temperature dependence of the equilibriawas measured forn = 1 to 5 in a pulsed electron beam mass spectrometer with a high pressure ion source. The ΔHn+1,nvalues obtained were (2,1) 15.4, (3,2) 9.1, (4,3) 8.4, (5,4) 6.7 kcal/mol. Possible structures of the clustered ions are proposed.Addition of water vapor leads to mixed cluster ions such as H+(H2S)x(H2O)y, withx + yfrom 1 to 6, observed as the ion source temperature was decreased to −100 °C. The temperature dependence of the equilibria for the exchange reactionsand the association reactionwere also measured. For all ions measured, the hydration process is energetically more favorable than the solvation by H2S.