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.

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The reaction of CHF 3 (HFC-23) with H atoms has been investigated by using a shock tube-atomic resonance absorption spectroscopy technique over the temperature range 1100-1350 K and the total concentration range 5.5 × 10 18 -8.5 × 10 18 molecules cm -3 . Ethyl iodide was used as a precursor of hydrogen atoms. The rate coefficient for the reaction CHF 3 + H f CF 3 + H 2 (1a) was determined from the decay profiles of H-atom concentration to be k 1a ) 10 -9.80(0.10 exp [-(64.6 ( 2.3) kJ mol -1 /RT] cm 3 molecule -1 s -1 (error limits at the 1 standard deviation level), which is 50-60% smaller than the value recommended by the NIST group. The rate coefficient was also calculated with the transition-state theory (TST). Structural parameters and vibrational frequencies of the reactants and transition state required for the TST calculation were obtained from an ab initio molecular orbital (MO) calculation. The energy barrier, E 0 q , which is the most sensitive parameter in the calculation, was adjusted until the TST rate coefficient most closely matched the observed one. This fitting yielded E 0 q) 59.0 kJ mol -1 , in excellent accord with the barrier of 62.0 kJ mol -1 calculated with the ab initio MO method at the G2(MP2) level.

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