Computer-aided mathematical calculations, simulating the mole fractions of C, C2H2, C2H and C-2 species, which are found present in the plasma during diamond growth, along the substrate radial length have been presented in this paper. Three different DC arc plasma jet powers, 16, 18 and 20 kW, were employed during this investigation. The purpose of this study was to investigate the effects of these plasma species on crystal size and film growth rate at different plasma powers. The simulations were coupled with experimental work, where polycrystalline diamond films were deposited onto molybdenum substrates using DC arc plasma jet chemical vapor deposition system. The computer-obtained results revealed that there is a noticeable variation in the mole fraction of each plasma species found above and along the radial distance of the substrate. Experimental results show that the average diamond grain size and the growth rate increase with input plasma power. However, the grain size and the growth rate, at any one plasma power, along the substrate radial distance remained constant. (C) 2003 Elsevier Science B.V. All rights reserved.