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621.
Jens Sehested Lene K. Christensen Ole J. Nielsen Timothy J. Wallington 《国际化学动力学杂志》1998,30(12):913-921
Using a pulse-radiolysis transient UV–VIS absorption system, rate constants for the reactions of F atoms with CH3CHO (1) and CH3CO radicals with O2 (2) and NO (3) at 295 K and 1000 mbar total pressure of SF6 was determined to be k1=(1.4±0.2)×10−10, k2=(4.4±0.7)×10−12, and k3=(2.4±0.7)×10−11 cm3 molecule−1 s−1. By monitoring the formation of CH3C(O)O2 radicals (λ>250nm) and NO2 (λ=400.5nm) following radiolysis of SF6/CH3CHO/O2 and SF6/CH3CHO/O2/NO mixtures, respectively, it was deduced that reaction of F atoms with CH3CHO gives (65±9)% CH3CO and (35±9)% HC(O)CH2 radicals. Finally, the data obtained here suggest that decomposition of HC(O)CH2O radicals via C C bond scission occurs at a rate of <4.7×105 s−1. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 913–921, 1998 相似文献
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623.
Jens Sehested Knud Sehested Jesper Platz Helge Egsgaard Ole John Nielsen 《国际化学动力学杂志》1997,29(8):627-636
The rate constant for the reaction of CH3OCH2 radicals with O2 (reaction (1)) and the self reaction of CH3OCH2 radicals (reaction (5)) were measured using pulse radiolysis coupled with time resolved UV absorption spectroscopy. k1 was studied at 296K over the pressure range 0.025–1 bar and in the temperature range 296–473K at 18 bar total pressure. Reaction (1) is known to proceed through the following mechanism: CH3OCH2 + O2 ↔ CH3OCH2O2# → CH2OCH2O2H# → 2HCHO + OH (kprod) CH3OCH2 + O2 ↔ CH3OCH2O2# + M → CH3OCH2O2 + M (kRO2) k = kRO2 + kprod, where kRO2 is the rate constant for peroxy radical production and kprod is the rate constant for formaldehyde production. The k1 values obtained at 296K together with the available literature values for k1 determined at low pressures were fitted using a modified Lindemann mechanism and the following parameters were obtained: kRO2,0 = (9.4 ± 4.2) × 10−30 cm6 molecule−2 s−1, kRO2,∞ = (1.14 ± 0.04) × 10−11 cm3 molecule−1 s−1, and kprod,0 = (6.0 ± 0.5) × 10−12 cm3 molecule−1 s−1, where kRO2,0 and kRO2,∞ are the overall termolecular and bimolecular rate constants for formation of CH3OCH2O2 radicals and kprod,0 represents the bimolecular rate constant for the reaction of CH3OCH2 radicals with O2 to yield formaldehyde in the limit of low pressure. kRO2,∞ = (1.07 ± 0.08) × 10−11 exp(−(46 ± 27)/T) cm3 molecule−1 s−1 was determined at 18 bar total pressure over the temperature range 296–473K. At 1 bar total pressure and 296K, k5 = (4.1 ± 0.5) × 10−11 cm3 molecule−1 s−1 and at 18 bar total pressure over the temperature range 296–523K, k5 = (4.7 ± 0.6) × 10−11 cm3 molecule−1 s−1. As a part of this study the decay rate of CH3OCH2 radicals was used to study the thermal decomposition of CH3OCH2 radicals in the temperature range 573–666K at 18 bar total pressure. The observed decay rates of CH3OCH2 radicals were consistent with the literature value of k2 = 1.6 × 1013exp(−12800/T)s−1. The results are discussed in the context of dimethyl ether as an alternative diesel fuel. © 1997 John Wiley & Sons, Inc. 相似文献
624.
Sarka Langer Evert Ljungstrm Ingvar Wngberg Timothy J. Wallington Michael D. Hurley Ole John Nielsen 《国际化学动力学杂志》1996,28(4):299-306
The rate constants for the gas-phase reactions of di-tert-butyl ether (DTBE) with chlorine atoms, hydroxyl radicals, and nitrate radicals have been determined in relative rate experiments using FTIR spectroscopy. Values of k(DTBE+CI) = (1.4 ± 0.2) × 10−10,k(DTBE+OH) = (3.7 ± 0.7) × 10−12, and k(DTBE+N03) = (2.8 ± 0.9) × 10−16 cm3 molecule−1 s−1 were obtained. Tert-butyl acetate was identified as the major product of both Cl atom and OH radical initiated oxidation of DTBE in air in the presence of NOx. The molar tert-butyl acetate yield was 0.85 ± 0.11 in the Cl atom experiments and 0.84 ± 0.11 in OH radical experiments. As part of this work the rate constant for reaction of Cl atoms with tert-butyl acetate at 295 K was determined to be (1.6 ± 0.3) × 10−11 cm3 molecule−1 s−1. The stated errors are two standard deviations (2σ). © 1996 John Wiley & Sons, Inc. 相似文献
625.
Ole Swang Knut Faegri Odd Gropen Ulf Wahlgren 《International journal of quantum chemistry》1996,57(1):105-111
The chemisorption of atomic hydrogen and oxygen on a cobalt surface has been studied on a five-atom cluster model using one-electron effective core potential (1e−ECP) and all-electron calculations at the ab initio SCF and MCPF levels. Also, density functional calculations have been carried out. The different approaches are evaluated. The 1e−ECP has been compared to similar ECPS for nickel and copper. Our results indicate that this approach is valid also for cobalt. Different contributions to the cluster-adsorbate bonding energy are discussed. © 1996 John Wiley & Sons, Inc. 相似文献
626.
627.
628.
The atmospheric chemistry of CCl2FCH2CF3 (HFCF-234fb) was examined using FT-IR/relative-rate methods. Hydroxyl radical and chlorine atom rate coefficients of k(CCl2FCH2CF3+OH)= (2.9 ± 0.8) × 10−15 cm3 molecule–1 s–1 and k(CCl2FCH2CF3+Cl)= (2.3 ± 0.6) × 10−17 cm3 molecule–1 s–1 were determined at 297 ± 2 K. The OH rate coefficient determined here is two times higher than the previous literature value. The atmospheric lifetime for CCl2FCH2CF3 with respect to reaction with OH radicals is approximately 21 years using the OH rate coefficient determined in this work, estimated Arrhenius parameters and scaling it to the atmospheric lifetime of CH3CCl3. The chlorine atom initiated oxidation of CCl2FCH2CF3 gives C(O)F2 and C(O)ClF as stable secondary products. The halogenated carbon balance is close to 80% in our system. The integrated IR absorption cross-section for CCl2FCH2CF3 is 1.87 × 10−16 cm molecule−1 (600–1600 cm−1) and the radiative efficiency was calculated to 0.26 W m−2 ppb1. A 100-year Global Warming Potential (GWP) of 1460 was determined, accounting for an estimated stratospheric lifetime of 58 years and using a lifetime-corrected radiative efficiency estimation. 相似文献