The use of hydrogen-rich CF4 plasmas leads to the selective etching of SiO2 in the presence of Si. The mechanisms which control this selectivity are poorly understood, and much more needs to be known about the fundamental chemical processes. In this work the reactions $$\begin{gathered} CF_3 + H \to CF_2 + HF \hfill \\ CF_2 + H \to CF + HF \hfill \\ \end{gathered} $$ have been studied at 295 K using a gas-flow reactor sampled by a mass spectrometer. The rate coefficients obtained are (8.9±1.8)×10−11 cm3 s−1 and (1.65±0.40)×10−13 cm3 s−1 for reactions (3) and (4) respectively. These values establish reaction (3) as a major source of CF2 while reaction (4) would be expected to be only a minor loss process in the etching environment.