AbstractThe high‐pressure collisional activation mass spectra with methane as the reagent/collision gas are reported for five aromatic halides. The major decomposition of the protonated aromatic halides is hydrogen halide elimination. The energy‐resolved mass spectra and the chemical reactivities of fragment ions with the methane collision gas are used to establish dissociation pathways and structures of fragment ions. The high‐pressure collisional activation mass spectra are compared with conventional collisionally induced dissociation and chemical ionization mass spectra.