In situ Fourier transform infrared spectroscopy was used to study the powder formation of hexamethyldisiloxane/O-2 plasmas. The spectra show that oxygen plays an important role at the beginning of the process. A large amount of oxygen is responsible for intense powder formation. The admixture of inert or non-reactant gases, such as AT or N-2, into the plasma promotes polymerization of the monomer. The formation of the particulates, the evolution of their size, and chemical characteristics give evidence of a multistep growth process. The size, as well as the production rate, undergoes a reduction once the Ar or N-2 amount is increased in the plasma admixture.