Ahtact: An FTICR mass spectrometry study has shown that gas-phase protonation of 1-fluoroand 1-chloroadamantane is followed by a carbon-halogen bond fission. This technique has also allowed the determination of the onset of these dissociative proton attachment reactions. The experimental findings are ratified by ab initio MO calculations showing that the equilibrium conformation of both protonated species correspond to an ion-dipole complex between the adamantyl cation and the corresponding hydrogen halide molecule. Both the theoretical and the experimental approaches indicate 1-fluoroadamantane to be more basic in thegas phase than 1 -chloroadamantane. The structures and harmonic vibrational frequencies of the relevant species in these reactions are also examined.