The adsorption of CCl 4 on Si(111)7×7 at room temperature has been characterized by electronic and vibrational electron energy loss spectroscopy (EELS). CCl 4 was found to adsorb dissociatively on Si(111)7×7 with the formation of SiCl bond and adsorbed CCl x species. At high exposures, CCl 4 appears to more readily undergo a greater degree of dechlorination. Using a Si 16 H 18 cluster to model only the adatom–restatom site, our density functional theory calculations suggest two plausible adstructures involving the dissociated Cl and CCl 3 fragments. The wavenumbers of the observed EELS features are found to be in general accord with the corresponding calculated wavenumbers. Thermal evolution of the adsorbed fragments has been followed by both vibrational and electronic EELS as a function of the sample annealing temperature. A new EELS feature at 920–960cm −1 attributed to SiC film or alloy formation is found to emerge at 573K, while the SiCl stretch at 550cm −1 , corresponding to dissociated surface Cl, is removed upon annealing to ∼883K. Furthermore, the electronic EELS spectra reveal an energy loss at 9.3eV that can be assigned to a single-electron transition from the Cl(p z ) bonding state to the Cl(p z ) antibonding state produced by the SiCl bond.