An extensive set of laser-induced fluorescence (LIF) measurements of Si atoms during the chemical vapor deposition (CVD) of silicon from silane and disilane in a research rotating disk reactor are presented. The experimental results are compared in detail with predictions from a numerical model of CVD from silane and disilane that treats the fluid flow coupled to gas-phase and gas-surface chemistry, The comparisons showed that the unimolecular decomposition of SiH2 could not account for the observed gas-phase Si atom density profiles. The H3SiSiH <-> Si + SiH4 and H3SiSiH + SiH2 <-> Si + Si2H6 reactions are proposed as the primary Si atom production routes. The model is in good agreement with the measured shapes of the Si atom profiles and the trends in Si atom density with susceptor temperature, pressure, and reactant gas mixture.