Thermal Decomposition of 1,1,1-Trifluoroethane Revisited

Abstract

1,1,1-Trifluoroethane (CH3CF3) has been frequently used as a chemical thermometer or an internal standard in shock tube studies to determine relative rates of chemical reactions. The rate constants for the thermal decomposition of CH3CF3 were recently reported to have anomalous pressure dependence in the high-temperature falloff region. In the present study, the kinetics of the CH3CF3 decomposition were reinvestigated using shock tube/laser absorption (ST/LA) spectroscopy and single-pulse shock tube (SPST) methods over the temperature range 1163-1831 K at pressures from 95 to 290 kPa. The present rate constants are 2-3 times smaller than those reported in previous single-pulse experiments performed at near high-pressure limit conditions. The recommended rate constant expression, k = 5.71 × 10(46)T(-9.341) exp(-47073 K/T) s(-1), was obtained over the temperature range 1000-1600 K with uncertainties of ±40% at temperatures below 1300 K and ±32% at 1600 K. The rate constants at the high-temperature region showed clear falloff behavior and were in good agreement with recent high-temperature experiments. The falloff rate constants could not be reproduced by a standard RRKM/master-equation model; this study provides additional evidence for the unusual pressure dependence previously reported for this reaction. Additionally, the rate constants for the decomposition of 1,1-difluoroethylene (CH2CF2) were determined over the temperature range 1650-2059 K at pressures of 100 and 205 kPa, and were reproduced by the RRKM/master-equation calculation with an average downward energy transfer of 900 cm(-1).

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

“…Figure 9 shows the Arrhenius plot of the master equation rate constants together with the corrected ST/LS data and those of the ST/LA experiment. 7 The calculated data at 2.0, 4.7, and 13 kPa were obtained with a Kr bath, and the others were obtained with Ar. The ST/TOF-MS data 6 are not shown here for the sake of simplicity because they quantitatively coincide with the ST/LA data.…”

Theoretical Study of the Rate Coefficients for CH3NHNH2 + NO2 and Related Reactions

“…The single‐point energies at optimized structures were refined by explicitly correlated RHF‐UCCSD(T)‐F12 method with the VDZ‐F12 basis sets by using Molpro 2012.1 program package. The vibrational frequencies used in the zero‐point correction and partition function calculations were calculated at the ωB97X‐D/6‐311++G(d,p) level of theory scaled by 0.975 and 0.950, respectively . The optimized geometries, rotational constants, and harmonic frequencies of the most stable isomers for the reactants, products, intermediates, and the transition states are listed in Tables S1 and S2 in the Supporting Information.…”

Experimental speciation study of natural gas oxidation using a single pulse shock tube

“…Temperature in the post shock reaction region is determined using chemical thermometers. 14,15 The post shock temperatures are calibrated using two chemical thermometers-1,1,1-trifluoroethane 16 (1200-1450 K) and cyclopropyl cyanide 17 (900-1150 K) whose unimolecular decomposition rates are well known. From the unimolecular decomposition the extent of reaction can be directly obtained by measuring the post shock decomposition of the chemical thermometer.…”