Kinetic and Spectroscopic Studies of the Reaction of CF₂ with H₂ in Shock Waves

The reaction of CF₂ with H₂ was studied in shock waves by monitoring UV absorption signals. CF₂ was prepared by thermal dissociation of C₂F₄ (or of c-C₃F₆). The rate constant of the reaction CF₂ + H₂ → CHF + HF near 2000 K was found to be close to 10¹¹ cm³ mol^-1 s^-1, consistent with earlier information on the reverse reaction CHF + HF → CF₂ + H₂ and a modeled equilibrium constant. The kinetic studies were accompanied by spectroscopic investigations. Absorption cross sections of C₂F₄ between 190 and 220 nm were measured near 1000 K and compared with room-temperature values from the literature. Likewise, absorption cross sections of CF₂ near 2000 K were measured between 210 and 300 nm and compared with room-temperature data. Additional superimposed absorption signals were recorded during the reaction and identified by their time dependence and by quantum-chemical calculations employing time-dependent density functional theory. A previously unknown absorption spectrum of CHF radicals near 200 nm was identified and its wavelength dependence determined. Further strong absorptions between 190 and 300 nm were attributed to CH₂F and CF radicals. Absorptions at longer wavelengths, reaching up to 510 nm, were postulated to arise from C₂ radicals formed at later stages of the reaction.