Electron-driven processes in the triclosan molecule are studied under gas-phase conditions using dissociative electron attachment (DEA) spectroscopy with the support of density functional theory calculations. Several decay channels of the short-lived (less than 17 μs) molecular anion of triclosan are associated with excitation of internal rotations of the phenyl rings around the C-O bonds. This leads to production of a dioxin anion by elimination of a neutral HCl molecule or negatively charged hypochlorous acid and dibenzofuran as the neutral counterpart. These decays are accompanied by cleavage and formation of several covalent bonds and appear on the microsecond timescale as confirmed by detection of metastable anions. On the basis of the present and earlier findings, DEA spectroscopy demonstrates to be a suitable technique for studying internal rotations in negative ions, although quite differently from the experimental techniques - microwave and Raman spectroscopies - usually employed to study internal rotations in neutral molecules.