The adsorption process of chlorine on Si(1 1 1) has been studied by means of real time surface differential reflectance (SDR) spectroscopy and second harmonic generation (SHG). The structure observed at 3.6 eV in SDR spectra is attributed to transitions including Si-Cl antibonding states. However, the overall feature is due to the removal of the electronic states of the clean surface. Developments of adsorption on Si adatom dangling bonds and breaking of adatom back bonds are obtained from SDR spectra and second harmonic (SH) intensity. They are well fit by the solutions of the rate equations under the assumption of adsorption of atoms without migration, and the initial sticking probability on the dangling bonds and the initial breaking probability of the back bonds are determined. Dependence of the adsorption kinetics on the carrier concentration is briefly reported.