Conventional and dynamic actinometric optical emission spectroscopies were used to investigate the composition of discharges of mixtures of tetramethylsilane, sulfur hexafluoride, and helium. Argon was present in a small proportion as an actinometer. Trends in the plasma concentrations of the species H, CH, Si, F, and CF2 were obtained as a function of the proportion of SF6 in the feed, R-s. Dynamic actinometry, which involves monitoring the relative intensities of plasma species following interruption of one of the principal feed gases, gave clues as to the relative importance of gas-phase and plasma/polymer-surface reactions in the production of the measured plasma species. Based on these data, reaction pathways and mechanisms for the production of these species are suggested.