The chemistry of the title cations was investigated in the gas phase by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry and by theoretical methods. Cl2H+ (1) was Obtained from the protonation of Cl-2 by gaseous Bronsted acids and the chlorination of HCl by Cl2F+ and XeCl+. The proton affinity (PA) of Cl-2 measured by the FT-ICR equilibrium method is 131.4 +/- 1 kcal mol(-1) at 298 K, which compares with the 132.0 kcal mol(-1) value computed at the CCSD(T) level of theory. 1 has the Cl-Cl-H connectivity, as indicated by its 2-fold reactivity as a Bronsted acid and a chlorinating agent, and confirmed by the theoretical results. The FClH+ cation was obtained from the fluorination of HCl by XeF+ and its most stable protomer (2) has the F-Cl-H connectivity, as shown by its behavior as a pure Bronsted acid and by the theoretical results that identify 2 as the global minimum, whereas protomer 3, having the H-F-Cl connectivity, is computed to be less stable by 5.0 kcal mol(-1) at the CCSD(T) level of theory, respectively. For lack of sufficiently accurate experimental data, the best estimate of the PA of ClF is 121.0 kcal mol(-1), computed at the CCSD(T) level of theory and referred to protonation of the Cl atom.