Kinetic Studies on the Reactions of CF₃ with O(³P) and H Atoms at High Temperatures

Abstract

The kinetics of the high-temperature reactions of CF 3 radicals with O( 3 P) and H atoms has been investigated experimentally and theoretically. The product channels of the CF 3 + O( 3 P) and CF 3 + H reactions were examined by calculating their branching fractions with the multichannel Rice-Ramsperger-Kassel-Marcus (RRKM) theory. Structural parameters, vibrational frequencies, and threshold energy required for the RRKM calculation were obtained from an ab initio MO calculation. The theoretical calculation showed that the productions of CF 2 O + F and CF 2 ( 1 A 1 ) + HF were the unique possible channels for the CF 3 + O( 3 P) and CF 3 + H reactions, respectively, and that the other channels such as deactivation were negligible for both the reactions. The rate coefficients for these reactions were experimentally determined by using a shock tubeatomic resonance absorption spectroscopy technique over the temperature ranges of 1900-2330 and 1150-1380 K and the total density ranges of 8.2 × 10 18 -1.2 × 10 19 and 6.1 × 10 18 -9.8 × 10 18 molecules‚cm -3 . Nitrous oxide and ethyl iodide were used as precursors of electronically ground-state oxygen and hydrogen atoms, respectively. Trifluoromethyl radicals were produced through the thermal dissociation of CF 3 I. The rate coefficients for the reactions CF 3 + O( 3 P) f CF 2 O + F (1b) and CF 3 + H f CF 2 ( 1 A 1 ) + HF (2c) were obtained from the decay profiles of O-and H-atom concentrations as k 1b ) (2.55(0.23) × 10 -11 and k 2c ) (8.86(0.32) × 10 -11 cm 3 molecule -1 s -1 (error limits at the one standard deviation level). Neither rate coefficient had any temperature or pressure dependence under the present experimental conditions; the values were in good agreement with some room-temperature data reported previously.

Shock‐tube studies on the reactions of dimethyl ether with oxygen and hydrogen atoms

“…Calibration experiments were performed behind reflected shock waves in 0.5–64 ppm N 2 O/Ar mixtures for the O‐atom ARAS and in 0.5 to 2 ppm C 2 H 5 I/Ar mixtures for the H‐atom ARAS. Details of the principles and procedures have been described elsewhere 20,21. The calibration results could not follow the Lambert–Beer law, due to self‐absorption or self‐reversal.…”

A chemical kinetic mechanism for combustion and flame propagation of CH2F2/O2/N2 mixtures

“…We ultimately selected an intermediate rate expression and have estimated an uncertainty factor of f = 1.8. For this rate expression, the A factor and E are about 2.5 and 2.8 times lower than those for the rate expression for CH 106 determined a rate constant of (5.3 ± 0.2) × 10 13 cm 3 mol −1 s −1 at 1150-1380 K, independent of temperature and pressure. That work used the simultaneous shock-induced thermal decompositions of CF 3 I and C 2 H 5 I to create CF 3 and H, respectively, in dilute argon and then derived rate constants on the basis of H atom decay rates monitored with atomic resonance absorption spectroscopy (ARAS).…”

Decomposition Mechanism of Fluorinated Compounds in Water Plasmas Generated Under Atmospheric Pressure

“…Unit for decomposition rate is mol cm -3 s -1 be measured experimentally. The reactions which have high possibilities in the thermal plasmas are described in Table 2 involving 20 species and 17 reaction steps [10,[24][25][26][27][28][29][30][31][32][33][34][35][36][37]. The rate reaction constants were calculated at a temperature of 2,000 K which is estimated from thermodynamic calculation.…”