Rate constants and Arrhenius parameters for the reactions of OH radicals and Cl atoms with CF3CH2OCHF2, CF3CHClOCHF2 and CF3CH2OCClF2, using the discharge-flow/resonance fluorescence method (original) (raw)
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The Journal of Chemical Physics, 1983
Cross sections, quantum yields, and threshold energies for the production ofUV and visible emission bands of CF 3 from photodissociation of CF3Br and CF 3 Cl were measured in the 115-130 nm region. The quantum yields for the production ofUV and visible emission bands for 0.2-1.0 and 1%-5%, respectively, both for the photolysis of CF3Br and CF 3 Cl. Appearance energies of the UV and visible emission are (9.41 ±0.05) and (9.39±0.02) eV, respectively, in the photolysis ofCF 3 Br and (1O.1O±0.08) and (1O.08±0.07) eV, respectively, in the case of CF 3CI. These results show that the upper state energies of the UV and visible emissions are very close to 6.4 eV above the CF 3 ground state. Potential energy surfaces of CF 3 radicals were calculated by the ab initio CI method. Possible transitions suggested for the UV and visible emission bands are 2A' 1 (Rydberg state)-+IA' 2 (ground state) and IE' and/or 2A' 2 (both are Rydberg states)-+I A'I (Rydberg state), respectively. These upper states 2A'I' IE', and 2A' 2' are most stable in theD 3h structure.
Rate constant for the reactions of CF3OCHFCF3 with OH and Cl
Chemical Physics Letters, 2000
The kinetics of reactions of CF OCHFCF with hydroxyl radicals and chlorine atoms has been investigated using a 3 3 discharged flow combined with both mass spectrometer and resonance fluorescence technique and using a relative rate technique, respectively, at 298 K. The rate constant for the reactions of CF OCHFCF with OH and Cl was determined to be 3 3 Ž. y15 3 y1 y1 Ž. y14 3 y1 y1 k s 4.98 " 1.64 = 10 cm molecule s and k s 3.1 " 2.5 = 10 cm molecule s , respectively. On the 1 2 basis of our kinetics measurements, the tropospheric lifetime of CF OCHFCF is calculated to be about 8 years, primarily 3 3 due to reaction with the hydroxyl radicals in the troposphere.
Photochemistry of fluorinated compounds: reaction between FCO and CF3CF2 radicals
Journal of Photochemistry and Photobiology A: Chemistry, 2002
CF 3 CF 2 C(O)F is a suitable source to generate the title radicals which can recombine to give back the precursor or lead to the formation of C 4 F 10 , CF 2 O and CO. We performed the photolysis of CF 3 CF 2 C(O)F pure and in the presence of c-C 6 H 12 or (FCO) 2 (oxalylfluoride), following the concentration of the different species by FTIR spectroscopy. The rate constant for the reaction CF 3 CF 2 + FCO → CF 3 CF 2 C(O)F was obtained through a simulation using both our experimental data and bibliography data available. The value found is (6.8 ± 0.8) × 10 −12 cm 3 molecule −1 s −1 and it is not substantially different from the rate constant (4.2 ± 0.5) × 10 −12 cm 3 molecule −1 s −1 obtained for the reaction of CF 3 and FCO radicals. Thus, it was concluded that the length of the carbon chain does not affect the mechanism nor the rate constant value when it is compared with the CF 3 + FCO system.
A DFT study on kinetics of the gas phase reactions of CH3CH2OCF3 with OH radicals and Cl atoms
Journal of Fluorine Chemistry, 2014
A theoretical study on the mechanism and kinetics of the gas phase reactions of CH 3 CH 2 OCF 3 (HFE-263) with the OH radicals and Cl atoms have been performed using meta-hybrid density functional MPWB1K method and 6-31+G(d,p) basis set. Energetics are further refined by calculating the energy of the species with a high level G2(MP2) method. Reaction profiles are modeled including the formation of pre-reactive and post-reactive complexes at entrance and exit channels. The hydrogen abstraction from -CH 2 group is found to be the dominant reaction channel for reaction with OH radicals, whereas hydrogen abstraction from CH 3 group is the dominant channel for Cl atoms, especially at higher temperature. Using groupbalanced isodesmic reactions, the standard enthalpies of formation for CH 3 CH 2 OCF 3 and radicals generated by hydrogen abstraction, CH 3 CHOCF 3 and CH 2 CH 2 OCF 3 are reported for the first time. The calculated bond dissociation energies for C-H bonds are in good agreement with experimental results. The rate constants of the two reactions are determined for the first time in a wide temperature range of 250-1000 K. The G2(MP2) calculated rate constant values are 0.52 Â 10 À13 and 0.77 Â 10 À12 cm 3 molecule À1 s À1 , respectively for reactions with OH radicals and Cl atoms at 298 K. ß
Kinetics of the reactions of FC(O)O2 radicals with F atoms and F2
Chemical Physics, 2000
The kinetics and the mechanism of the 248 nm laser¯ash photolysis of oxalyl¯uoride, (FCO) 2 , in the presence of O 2 , F 2 and the bath gases He and SF 6 has been studied at 295 K. The kinetics was followed by monitoring the FC(O)O radical by absorption at 545 nm. Rate coecient values of 3X4 AE 0X7 Â 10 À15 and 4X5 AE 0X7 Â 10 À12 cm 3 molecule À1 s À1 were determined for the reactions FCOO 2 F 2 3 FCOOOF F and FCOO 2 F 3 FCOO OF, whereas the upper limits of 1 Â 10 À17 and 9 Â 10 À14 cm 3 molecule À1 s À1 were estimated for FCOO F 2 3 FCOOF F and FCOO FO 2 3 FCOOF O 2 . From isodesmic reaction schemes at the B3LYP/6-311++G(d,p) level of theory, the enthalpies of formation of FCO, FC(O)OF, FC(O)OOF and FC(O)OOO(O)CF were calculated to be À44X6 AE 2, À102X9 AE 2, À91X2 AE 2 and À186X0 AE 2 kcal mol À1 , respectively. Density functional theory and statistical adiabatic channel model calculations allow us to establish that the reaction between F atoms and FC(O)O 2 proceeds through the formation of an energized complex FC(O)OOF towards FC(O)O and OF in agreement with the experiments. Ó .ar (C.J. Cobos).
Computational and Theoretical Chemistry, 2013
Theoretical investigations were carried out on the mechanism, kinetics and thermochemistry of the gasphase reactions between CHF 2 CF 2 OCHF 2 and OH radical using the high level ab initio G2(MP2) and hybrid density functional MPWB1K/6-31+G(d,p) methods. Two most stable conformers of CHF 2 CF 2 OCHF 2 are identified and the energy difference between them is found to be only 0.3 kcal mol À1. Both of them are considered for rate coefficient calculations in our study and the contribution from each of the conformers is found to be quite significant in the temperature range of our study. The rate coefficients are determined for the first time in a wide range of temperature 250-1000 K. The calculated total rate coefficient value k OH = 1.01 Â 10 À15 cm 3 molecule À1 s À1 is in reasonably good agreement with the experimental value of k OH = 2.36 Â 10 À15 cm 3 molecule À1 s À1 at 298 K. The heats of formation for CHF 2 CF 2 OCHF 2 and CHF 2 CF 2-OCF 2 and CF 2 CF 2 OCHF 2 radicals are estimated to be À359.64, À305.43 and À306.88 kcal mol À1 , respectively. The bond dissociation energies of the two C-H bonds are CHF 2 CF 2 OC(-H)F 2 : 106.3 kcal mol À1 and C(-H)F 2 CF 2 OCHF 2 : 104.8 kcal mol À1. The atmospheric lifetime of CHF 2 OCF 2 CHF 2 is estimated to be around 35 years.
Rate Measurement of the Reaction of CF2Cl Radicals with O2
Photochemistry and Photobiology, 2006
We have studied the association reaction of the CFzCl radicals with Oz in presence of Nz. The infrared multiple photon dissociation (IRMPD) technique with a homemade TEA COz laser was used for the CFzCI radical generation and the vibrational chemiluminiscence technique was set up for the study of the reaction kinetics. The time-resolved IR fluorescence of the vibrationally excited CFzO photoproduct was used to measure the disappearance rate of these radicals. A kinetic mechanism is presented to account for the rate of production of CF20*. The CFzCl radical association reaction rate with Oz, evidence of a direct channel of photoproduct formation and its reaction rate, and the CFzO* collisional deactivation rate have been obtained.