Kinetic Studies on the Reactions of Heptafluoropropanes with O(3P) and H Atoms at High Temperatures
Kinetic Studies on the Reactions of Heptafluoropropanes with O(3P) and H Atoms at High Temperatures
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DOI：
10.1021/jp036669k
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发表时间：
2004-01
影响因子：
2.9
通讯作者：
O. Yamamoto;Kazuo Takahashi;T. Inomata
中科院分区：
文献类型：
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作者：
O. Yamamoto;Kazuo Takahashi;T. Inomata
用激波管技术结合原子共振吸收光谱研究了2H-七氟丙烷(CF3CHFCF3，HFC-227ea)与O(3P)和H原子在高温下的反应。二氧化硫的激光光解和碘乙烷的热分解分别产生了电子基态氧原子和氢原子。由O(3P)和H原子的衰变实验测定了反应CF3-CHFCF3+O(3P)→I-C3F7+OH(1a)和CF3CHFCF3+H→I-C3F7+H2(2a)的速率系数.2 7‘0。6.7exp[-(56‘13)kJmol-1/RT]cm3分子-1 S-1(880-1180K)，k2a=10-9。1 5‘0。6 6exp[-(63‘14)kJmol-1/RT]cm3分子-1 S(1000-1180K)。这些结果表明，在本实验温度范围内，反应2a比反应1a快7-8倍。由于氟原子的电子吸引效应，丙烷与O(3P)和H原子反应的速率系数都比以前的动力学数据小得多。为了比较异构体之间的反应活性，还用同样的方法测定了1H-七氟丙烷CHF2CF2CF3+O(3P)→n-C3F7+OH(3a)和CHF2CF2CF3+H→n-C3F7+H2(4a)的反应速率系数。1 3‘0。52exp[-(55‘10)kJmol-1/RT]cm3分子-1 S(880-1180K)，k4a=10-9。4 4‘0。32exp[-(57‘7)kJmol-1/RT]cm3分子-1 S(1000-1180K)。用过渡态理论(TST)计算了反应1a和2a的速率系数。通过MP2(Full)/6-31G(D)从头算分子轨道(MO)计算得到了反应物的结构参数、振动频率和TST计算所需的过渡态。调整能垒E0，直到TST速率系数与观察到的最接近。E0(1a)=51kJ·mol-1和E0(2a)=41kJ·mol-1的拟合结果与G2(MP2)势垒在预期的不确定度范围内一致。
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) → i-C 3 F 7 + OH (la) and CF 3 CHFCF 3 + H → i-C 3 F 7 + H 2 (2a) were experimentally determined from the decay of O( 3 P) and H atoms as k 1 a = 10 - 1 0 . 2 7 ′ 0 . 6 7 exp[-(56 ′ 13) kJ mol - 1 /RT] cm 3 molecule - 1 s - 1 (880-1180 K) and k 2 a = 10 - 9 . 1 5 ′ 0 . 6 6 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 1H-heptafluoropropane, CHF 2 CF 2 CF 3 + O( 3 P) → n-C 3 F 7 + OH (3a) and CHF 2 CF 2 CF 3 + H → n-C 3 F 7 + H 2 (4a), were also determined by using the same technique as k 3 a = 10 - 1 0 . 1 3 ′ 0 . 5 2 exp[-(55 ′ 10) kJ mol - 1 /RT] cm 3 molecule - 1 s - 1 (880-1180 K) and k 4 a = 10 - 9 . 4 4 ′ 0 . 3 2 exp[-(57 ′ 7) kJ mol - 1 /RT] cm 3 molecule - 1 s - 1 (1000-1180 K). Furthermore, the rate coefficients for reactions la and 2a 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 (1a) = 51 kJ mol - 1 and E 0 (2a) = 41 kJ mol - 1 were in agreement with the G2(MP2) energy barriers, within the expected uncertainty.