Reaction of CF3 radicals on fused silica between 320 and 530 K

Abstract

The reaction between CF3 radicals and silicon oxide (fused silica) surface was studied in a VLPΦ flow reactor (∼0.1–3 mTorr) as functions of surface temperature (320–530 K) and CF3 concentration. The CF3 radicals were generated from CF3I by CO2 laser photolysis, and the subsequent gas-phase reaction products were followed by mass spectroscopy. The surface reaction was found to yield CO, HF, CO2, COF2, and SiF4. It was found that H2O residing on the silicon oxide surface was largely responsible for the oxygen- and hydrogen-containing products, and that little etching of the SiO2 itself occurred under these conditions. The rates for the irreversible surface loss of CF3, and for the formation of CO were both first order with respect to [CF3]. These were found to be temperature dependent with Ea≂4.7 and 7.5 kcal/mol, respectively. The CF3 surface loss rate indicates that the sticking coefficient for this radical on quartz is between 0.0014–0.017 for the temperature range of this study.