The diamond deposition on molybdenum substrate was examined in the Ar/H-2 dc plasma jet adding dichlorobenzene as the carbon source compared with adding benzene. Well-faceted, high quality diamond was formed on the substrate when dichlorobenzene was used as the carbon source. Graphite or amorphous carbon was not observed on the surface of the deposits by Raman spectroscopy, though the impurities were observed on the surface of the deposits from the plasma jet with benzene as the carbon source. A chlorine abstraction of surface-adsorbed hyhdrogen plays a dominant role in activating the diamond surface, which thus gives rise to higher diamond deposition rates and removal of graphite or amorphous carbon.