The reactions of 2H-heptafluoropropane (CF 3 CHFCF 3 , HFC-227ea) with O( 3 P) and H atoms have been studied at high temperatures by using a shock tube technique coupled with atomic resonance absorption spectroscopy. Electronically ground-state oxygen and hydrogen atoms were produced by the laser photolysis of sulfur dioxide and the thermal decomposition of ethyl iodide, respectively. The rate coefficients for the reactions CF 3 -CHFCF 3 + O( 3 P) f i-C 3 F 7 + OH (1a) and CF 3 CHFCF 3 + H f i-C 3 F 7 + H 2 (2a) were experimentally determined from the decay of O( 3 P) and H atoms as k 1a ) 10 -10.27(0.67 exp[-(56 ( 13) kJ mol -1 /RT] cm 3 molecule -1 s -1 (880-1180 K) and k 2a ) 10 -9.15(0.66 exp [-(63 ( 14) kJ mol -1 /RT] cm 3 molecule -1 s -1 (1000-1180 K). These results showed that reaction 2a was faster than reaction 1a by a factor of 7-8 over the present experimental temperature range. Both rate coefficients were much smaller than the previous kinetic data for the reactions of propane with O( 3 P) and H atoms, because of an electron-attracting effect of fluorine atoms. To compare the reactivities between isomers, the rate coefficients for the reactions of 1Hheptafluoropropane, CHF 2 CF 2 CF 3 + O( 3 P) f n-C 3 F 7 + OH (3a) and CHF 2 CF 2 CF 3 + H f n-C 3 F 7 + H 2 (4a), were also determined by using the same technique as k 3a ) 10 -10.13(0.52 exp[-(55 ( 10) kJ mol -1 /RT] cm 3 molecule -1 s -1 (880-1180 K) and k 4a ) 10 -9.44(0.32 exp[-(57 ( 7) kJ mol -1 /RT] cm 3 molecule -1 s -1 (1000-1180 K). Furthermore, the rate coefficients for reactions 1a and 2a were calculated with the transitionstate theory (TST). Structural parameters and vibrational frequencies of the reactants and the transition states required for the TST calculation were obtained from the MP2(full)/6-31G(d) ab initio molecular orbital (MO) calculation. The energy barrier, E 0 q , was adjusted until the TST rate coefficient most closely matched the observed one. The fitting results of E 0 q (1a) ) 51 kJ mol -1 and E 0 q (2a) ) 41 kJ mol -1 were in agreement with the G2(MP2) energy barriers, within the expected uncertainty.
Methyl formate is selectively produced in the dehydrogenation of methanol over Pd/ZnO; the reaction is suggested to proceed through the same steps as over copper-based catalysts.
The reactions of dimethyl ether (CH 3 OCH 3 , DME) with O( 3 P) and H atoms have been studied at high temperatures by using a shock tube apparatus coupled with atomic resonance absorption spectroscopy (ARAS). The rate coefficients for the reactions CH 3 OCH 3 + O( 3 P) → CH 3 OCH 2 + OH (1) and CH 3 OCH 3 + H → CH 3 OCH 2 + H 2 (2) were experimentally determined from the decay of O( 3 P) and H atoms as:These results show that DME can react with O( 3 P) atoms more easily than with H atoms. By combining these results with the previous lower temperature data, we obtained the following modified Arrhenius expressions applied over the wide temperature range between 300 and 1500 K: Both reactions of DME are faster than those of ethane, because the dissociation energy of the C H bond in DME is smaller. Furthermore, the rate coefficients for reactions (1) and (2) were calculated with the transition-state theory (TST). Structural parameters and vibrational frequencies of the reactants and the transition states required for the TST calculation were obtained from the MP2(full)/6-31G(d) ab initio molecular orbital (MO) calculation. The energy barrier, E ‡ 0 , was adjusted until the TST rate coefficient most closely matched the observed one. The fitting results of E ‡ 0 (1) = 23 kJ mol −1 and E ‡ 0 (2) = 34 kJ mol −1 were in agreement with the G2 energy barriers, within the expected uncertainty, demonstrating that the experimentally determined rate coefficients were theoretically valid. C 2006 Wiley Periodicals, Inc. Int J Chem Kinet
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