Infrared and electronic spectroscopy was applied to the benzene-ammonia cluster cation in the gas phase, and the observed spectra revealed the formation of a new C-N valence bond between the benzene and ammonia moieties, which has been predicted by the quantum chemical calculations ( Tachikawa, H. Phys. Chem. Chem. Phys. 2002, 4, 6018). This cluster cation is regarded as a model for the cyclohexadienyl type intermediate in nucleophilic substitution reactions.