Ion attachment mass spectrometry (IAMS) was used to analyze the species in cyclo-C4F8 plasma quantitatively. Not only stable neutral molecules but also less stable radicals were detected. Ions and species without a charge in the plasma were perfectly distinguishable. The measured dependence of the product distribution on the rf power shows that IAMS can be used to clarify and control the processes in the plasma. (c) 2006 American Vacuum Society.