Shock Tube Study on the Thermal Decomposition of Fluoroethane Using Infrared Laser Absorption Detection of Hydrogen Fluoride

Abstract

Motivated by recent shock tube studies on the thermal unimolecular decomposition of fluoroethanes, in which unusual trends have been reported for collisional energy-transfer parameters, the rate constants for the thermal decomposition of fluoroethane were investigated using a shock tube/laser absorption spectroscopy technique. The rate constants were measured behind reflected shock waves by monitoring the formation of HF by IR absorption at the R(1) transition in the fundamental vibrational band near 2476 nm using a distributed-feedback diode laser. The peak absorption cross sections of this absorption line have also been determined and parametrized using the Rautian-Sobel'man line shape function. The rate constant measurements covered a wide temperature range of 1018-1710 K at pressures from 100 to 290 kPa, and the derived rate constants were successfully reproduced by the master equation calculation with an average downward energy transfer, ⟨ΔEdown⟩, of 400 cm(-1).

Thermal Decomposition of 2,3,3,3- and trans-1,3,3,3-Tetrafluoropropenes

“…HF produced from the thermal decomposition of TFPs behind the reflected shock waves was detected by its IR absorption near 2476 nm. The HF concentration was calculated from Beer’s law using the absorption cross-section parametrized in the previous study, based on the Rausian–Sobel’man line profile, with the estimated uncertainty of 5% . The sample gases used were mixtures of 20 or 50 ppm of 2,3,3,3-TFP (>99% purity; Honeywell International Inc.) or trans -1,3,3,3-TFP (>99% purity; Honeywell International Inc.) diluted in Ar (>99.9999% purity; Taiyo Nippon Sanso).…”

“…The experiments were performed using a double-piston-actuated diaphragm-less shock tube. The apparatus and method have been described elsewhere, , and only specific details are presented here. HF produced from the thermal decomposition of TFPs behind the reflected shock waves was detected by its IR absorption near 2476 nm.…”

“…12,13 The most plausible explanation for this is that the unimolecular decomposition of the reactants first produced vibrationally excited HF, and its relaxation 41 is observed as the incubation period. 12,13,39 Since the HF profiles are considered to have a complex dependence on kinetics and pathways of the primary and secondary reactions, they were analyzed with the aid of computational investigations on the reaction mechanisms.…”

Dissociation of 1,1,1-Trifluoroethane Is an Intrinsic RRKM Process: Classical Trajectories and Successful Master Equation Modeling

“…67 An indication of the formation of vibrationally excited HF from R1 was also observed in the ST/LA experiment 7 as a short incubation period in the absorption profile of HF at the vibrationally ground state. 68 In the ST/LA study, rate constants for R1 were derived by interpreting the absorption profile using a kinetic model that included formation and relaxation of the vibrationally excited HF (denoted as HF* in ref 7). The model was rather primitive because the distribution of the vibrational quantum numbers were not taken into account; the model attributed all of the HF formed to be HF* that relaxes with the same rate constant, k HF−Ar .…”

The Unimolecular Reactions of CF3CHF2 Studied by Chemical Activation: Assignment of Rate Constants and Threshold Energies to the 1,2-H Atom Transfer, 1,1-HF and 1,2-HF Elimination Reactions, and the Dependence of Threshold Energies on the Number of F-Atom Substituents in the Fluoroethane Molecules

“…Both thermal − and chemical-activation methods − were used to characterize the Arrhenius parameters and the nature of the four-centered transition state. Electronic-structure calculations − have recently provided additional understanding of the transition states for C 2 H 5 F, C 2 H 4 F 2 , and CH 3 CF 3 , which permit more reliable assignments of threshold energies from rate constants measured at a specific energy. − High-temperature studies of CH 3 CH 2 F, CH 3 CF 3 , and CF 3 CHF 2 continue to receive attention with an emphasis on the collisional activation and deactivation models in the falloff region. − The 1,2-HF elimination reactions of fluoroethanes can be adequately described by statistical RRKM models for the vast majority of experimental conditions. ,, As H atoms are replaced by F atoms in the fluoroethane series, the threshold energy E 0 for 1,2-HF elimination increases; however, the correct E 0 values for the molecules with 4 and 5 fluorine atoms remain to be firmly established. Our laboratory has used the chemical activation technique to study CH 2 FCH 2 F, CH 2 FCHF 2 , and CHF 2 CHF 2 , and in the present work we report experiments for CF 3 CHF 2 .…”