Kinetic and Mechanistic Studies of the Reactions of CF3O Radicals with NO and NO2

Chr. Fockenberg, H. Somnitz, G. Bednarek, R. Zellner
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引用次数: 5

Abstract

The reactions of CF3O radicals with (1) NO and (2) NO2 were studied using two different experimental techniques. A laser photolysis/LIF detection method was applied for measuring the rate constants as a function of temperature (T = 222–302 K) and total pressure (ptot = 7–107 mbar). Whereas the reaction with (1) NO was found to be independent of temperature and pressure with k1 = (4.5±1.2)×10−11 cm3 s−1, the reaction with (2) NO2 was found to be dependent on both of these variables. The temperature dependence of k2 in the high pressure limit can be given by the expression k2,∝ (T) = (8±5)×10−13 exp ((863±194) K/T) cm3 s−1. The product distributions of the two reactions were determined in separate experiments using steady-state photolysis combined with FTIR spectroscopy. For reaction (1) only CF2O was found as a reaction product with a yield of 0.93±0.10, independent of temperature. For reaction (2) several products (CF3ONO2, CF2O, FNO2) were identified, the overall yield, however, is dominated (≥90%) by the recombination product CF3ONO2. A theoretical analysis of the detailed mechanisms of both reactions was made by performing ab initio energy and geometry predictions in combination with RRKM calculations. Both reactions were found to proceed via an initial addition mechanism involving the CF3ONOx (x = 1, 2) intermediate and a four-center transition state. A direct abstraction of an F atom by NO or NO2 can be excluded.

cf30自由基与NO和NO2反应的动力学和机理研究
采用两种不同的实验方法研究了cf30自由基与(1)NO和(2)NO2的反应。采用激光光解/LIF检测方法测定了速率常数随温度(T = 222 ~ 302 K)和总压(pot = 7 ~ 107 mbar)的变化规律。当k1 =(4.5±1.2)×10−11 cm3 s−1时,发现与(1)NO的反应与温度和压力无关,而与(2)NO2的反应则与这两个变量都有关。k2在高压极限下的温度依赖性可由表达式k2给出,∝(T) =(8±5)×10−13 exp((863±194)K/T) cm3 s−1。用稳态光解结合红外光谱法分别测定了两种反应的产物分布。对于反应(1),只有CF2O作为反应产物,产率为0.93±0.10,与温度无关。在反应(2)中,虽然鉴定出了几种产物(CF3ONO2、CF2O、FNO2),但总产率以重组产物CF3ONO2为主(≥90%)。通过结合RRKM计算进行从头算能量和几何预测,对两种反应的详细机理进行了理论分析。两个反应都是通过CF3ONOx (x = 1,2)中间体和四中心过渡态的初始加成机制进行的。可以排除由NO或NO2直接提取F原子的可能性。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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