Shock wave and modeling study of the reaction CF 4 (+M) ⇔ CF 3 + F (+M)

Hintzer²,

Sölter

et al. 2021

J. Phys. Chem. A

The thermal dissociation reactions of C 2 F 4 and C 2 F 6 were studied in shock waves over the temperature range 1000−4000 K using UV absorption spectroscopy. Absorption cross sections of C 2 F 4 , CF 2 , CF, and C 2 were derived and related to quantum-chemically modeled oscillator strengths. After confirming earlier results for the dissociation rates of C 2 F 4 , CF 3 , and CF 2 , the kinetics of secondary reactions were investigated. For example, the reaction CF 2 + CF 2 → CF + CF 3 was identified. Its rate constant of 10 10 cm 3 mol −1 s −1 near 2400 K is markedly larger than the limiting high-pressure rate constant of the dimerization CF 2 + CF 2 → C 2 F 4 , suggesting that the reaction follows a different path. When the measurements of the thermal dissociation CF 2 (+Ar) → CF + F (+Ar) are extended to temperatures above 2500 K, the formation of C 2 radicals was shown to involve the reaction CF + CF → C 2 F + F (modeled rate constant 8.0 × 10 12 (T/3500 K) 1.0 exp(−4400 K/T) cm 3 mol −1 s −1 ) and the subsequent dissociation C 2 F (+Ar) → C 2 + F + (Ar) (modeled limiting low-pressure rate constant 3.0 × 10 16 (T/3500 K) −4.0 exp(−56880 K/T) cm 3 mol −1 s −1 ). This mechanism was validated by monitoring the dissociation of C 2 at temperatures close to 4000 K. Temperature-and pressure-dependences of rate constants of reactions involved in the system were modeled by quantum-chemistry based rate theory.

Section: Secondary Reactions Inmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

High-Temperature Fluorocarbon Chemistry Revisited

Hintzer²,

Sölter

et al. 2021

J. Phys. Chem. A

“…This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made. © 2021 Wiley Periodicals LLC Knight et al, 3 who studied the dissociation,…”

Section: Introductionmentioning

confidence: 99%

“…However, because of the strength of the C–F bond, CF 4 requires high temperatures to be decomposed. For example, temperatures between 2000 and 3000 K were applied in the 2016 shock wave experiments of Knight et al., 3 who studied the dissociation,

\begin{matrix} true \\ left {CF}_{4} (() + M) \to {CF}_{3} + normalF (() + M) \\ left Δ_{r} H^{o} ((), 0, K) = 539.8 normalkJ normalmo l^{- 1} \end{matrix}

(values for the reaction enthalpies at 0 K, ∆ r H o (0 K), are from Goos et al 4…”

Section: Introductionmentioning

confidence: 99%

Theoretical modeling study of the reaction H + CF₄ → HF + CF₃

Int J of Chemical Kinetics

Knight

Marshall

et al. 2021

Self Cite

The high-temperature hydrogenation of CF 4 in mixtures of CF 4 and H 2 is assumed to involve the reaction H + CF 4 → HF + CF 3 . The hydrogen atoms here are either formed by the reaction of F and CF 3 (i.e., the products of the thermal dissociation of CF 4 ) with H 2 , or by the thermal dissociation of H 2 . In the former case, a complicated chain process is started, while the reaction proceeds in a more direct way in the latter. This article determines the rate constant of the reaction H + CF 4 → HF + CF 3 , characterizing its transition state by quantum-chemical methods. Over the temperature range 1000-3000 K, the most accurate results for the rate constant can be represented in the form 1.64 × 10 14 (T/1000 K) 1.95 exp(−178.8 kJ mol -1 /RT) cm 3 mol -1 s -1 , based on coupled cluster theory extrapolated to the complete basis set limit, and incorporating vibrational anharmonicity, electron correlation through CCSDT(Q), and relativistic and non-Born-Oppenheimer effects.

Practical Aspects of Thermal Dissociation and Recombination Reactions: The Reaction Systems CF₃X(+M)↔CF₃+X (+M) with X=F, Cl, Br, and I

Israel Journal of Chemistry

Tellbach

Sölter

et al. 2023

Self Cite

The thermal dissociation/recombination reactions of the perfluoromethyl halides CF4↔CF3+F, CF3Cl↔CF3+Cl, CF3Br↔CF3+Br, and CF3I↔CF3+I are analyzed with respect to their transition (for increasing pressures) from second‐order to first‐order dissociation (or from third‐order to second‐order recombination). The dependence of this transition on the temperature is documented. Practical aspects of the modelling of falloff curves are discussed.