1493-02-3Relevant articles and documents
Atmospheric Chemistry of CF3O Radicals: Reaction with H2O
Wallington, Timothy J.,Hurley, Michael D.,Schneider, William F.,Sehested, Jens,Nielsen, Ole John
, p. 7606 - 7611 (1993)
Evidence is presented that CF3O radicals react with H2O in the gas phase at 296 K to give CF3OH and OH radicals.This reaction is calculated to be exothermic by 1.7 kcal mol-1 implying a surprisingly strong CF3O-H bond energy of 120 +/- 3 kcal mol-1.Results from a relative rate experimental study suggest that the rate constant for the reaction of CF3O radicals with H2O lies in the range (0.2-40) x 10-17 cm3 molecule-1 s-1.Implications for the atmospheric chemistry of CF3O radicals are discussed.
Role of excited CF3CFHO radicals in the atmospheric chemistry of HFC-134a
Wallington,Hurley,Fracheboud,Orlando,Tyndall,Sehested,Mogelberg,Nielsen
, p. 18116 - 18122 (1996)
The atmospheric degradation of HFC-134a (CF3CFH2) proceeds via the formation of CF3CFHO radicals. Long path length FTIR environmental chamber techniques were used to study the atmospheric fate of CF3-CFHO radicals. Two competing reaction pathways were identified for CF3CFHO radicals: reaction with O2, CF3CFHO + O2 → CF3C(O)F + HO2, and decomposition via C-C bond scission, CF3CFHO + M → CF3 + HC(O)F + M. CF3CFHO radicals were produced by two different reactions: either via the self-reaction of CF3CFHO2 radicals or via the CF3CFHO2 + NO reaction. It was found that decomposition was much more important when CF3CFHO radicals were produced via the CF3CFHO2 + NO reaction than when they were produced via the self-reaction of CF3CFHO2 radicals. We ascribe this observation to the formation of vibrationally excited CF3CFHO* radicals in the CF3CFHO2 + NO reaction. Rapid decomposition of CF3-CFHO* radicals limits the formation of CF3C(O)F and hence CF3COOH in the atmospheric degradation of HFC-134a. We estimate that the CF3COOH yield from atmospheric oxidation of HFC-134a is 7-20%. Vibrationally excited alkoxy radicals may play an important role in the atmospheric chemistry of other organic compounds.
Atmospheric Chemistry of HFC-134a: Kinetic and Mechanistic Study of the CF3CFHO2 + HO2 Reaction
Maricq, M. Matti,Szente, Joseph J.,Hurley, Michael D.,Wallington, Timothy J.
, p. 8962 - 8970 (1994)
Rate constant measurements for the title reaction and for F + CF3CFH2 are reported over the 210-363 K temperature range.Reacting mixtures of CF3CFHO2 and HO2 radicals are created by the flash photolysis of F2 in the presence of HFC-134a (CF3CFH2), H2, and O2 and are probed by time-resolved UV absorption spectroscopy.The deconvolution of spectra taken at various delay times provides concentration versus time profiles for the respective radical species.A comparison of the initial CF3CFHO2 and HO2 concentrations yields a relative rate determination of k1 = (9.8+9-5) * 10-11e(-1130+/-190)/T cm3s-1 for the F + CF3CFH2 rate constant.A simultaneous fit of the radical decay curves to a mechanism containing the known HO2 self-reaction kinetics, the previously determined CF3CFHO2 self-reaction mechanism, and a cross reaction between these species yields a rate constant of k7 = (1.8+2.4-1.0) * 10-13e(910+/-220)/T cm3s-1 for the HO2 + CF3CFHO2 reaction.A product stucy at 296 K by Fourier transform infrared spectroscopy reveals that less than 5percent of the product appears as CF3C(O)F.By inference, >95percent of the reaction gives the hydroperoxide CF3CFHOOH.Implications of these results are discussed with respect to the atmospheric degradation of HFC-134a (CF3CFH2).
Rate Mechanism of the Atmospheric Degradation of 1,1,1,2-Tetrafluoroethane (HFC-134a)
Bednarek,Ereil,Hoffmann,Kohlmann,Moers,Zellner
, p. 528 - 539 (2007/10/03)
Ihe atmospheric chemical behaviour of 1,1,1,2-tetrafluoroethane (CF3CFH2, HFC-134a) with respect to its rate and mechanism of degradation in the troposphere has been investigated. The rate coefficient for the reaction of (i a) CF3CFH2 +OH→CF3CFH + H2O has been determined in direct time-resolved experiments using iaser-pulse initiation and laser long-path absorption. A value of kia = (4.6±0.5)×10-15 cm3 A at T = 295K has been found. The ratio of the rate coefficients for the reactions of the CF3CFHO-radical with O2, (4) CF3CFHO + O2→CF3CFO + HO2, and C-C bond fission, (5) CF3CFHO + M→CFHO + CF3 + M, for T =295 K and ptotal = 50 mbar (O2) has been obtained to be k4/(k5 [M]) = 1.5×10-19 cm3, with the individual values being k4 = 2.7×10-15 cm3/s and k5 [M] = 1.8×104 s-1. The mechanism of the atmospheric degradation of HFC-134a has been investigated in the temperature range 244-295 K and ptotal = 1000 mbar using UV photolysis/FTIR product studies. From these experiments the Arrhenius expression k4/(k5 [M]) = 8.7 ×10-25 exp ((3240-610+990) K/T) cm3 was determined. Moreover, it is concluded that the major carbonyl products are CF3CFO, CFHO and CF2O which result from the two possible reactions of the oxy radical CF3CFHO. As a consequence the yield of these carbonyl products is dependent on temperature, O2 partial pressure and total pressure. For the reaction of CFHO with Cl atoms the Arrhenius expression k18 = 5.7×10-14 exp (-(1130 ±160)K/T)cm3/s was determined in the temperature range 244-298 K. VCH Verlagsgeseuschaft mbH, 1996.
