Experimental and Theoretical Study on the OH-Reaction Kinetics and Photochemistry of Acetyl Fluoride (CH3C(O)F), an Atmospheric Degradation Intermediate of HFC-161 (C2H5F).
Experimental and Theoretical Study on the OH-Reaction Kinetics and Photochemistry of Acetyl Fluoride (CH3C(O)F), an Atmospheric Degradation Intermediate of HFC-161 (C2H5F).
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DOI：
10.1021/acs.jpca.5b01069
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发表时间：
2015-04
期刊：
影响因子：
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通讯作者：
Xinli Song;G. L. Zügner;M. Farkas;Á. Illés;D. Sarzyński;T. Rozgonyi;Baoshan Wang;S. Dóbé
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文献类型：
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作者：
Xinli Song;G. L. Zügner;M. Farkas;Á. Illés;D. Sarzyński;T. Rozgonyi;Baoshan Wang;S. Dóbé
采用共振荧光监测OH （RF）的低压快速排出流（DF）直接反应动力学方法，确定了OH + C2H5F (EtF)(1)和OH + CH3C(O)F (AcF)(2)总反应的速率系数。乙酰氟与羟基自由基反应缓慢，实验温度下的反应速率系数为k2(300 K) =（0.74±0.05）× 10(-14) cm(3)分子（-1）s(-1)（给出的统计不确定度为2σ）。反应的温度依赖性不符合Arrhenius定律，可以用双指数速率表达式k2(300-410 K) = 3.60 × 10(-3) exp(-10500/T) + 1.56 × 10(-13) exp(-910/T) cm(3)分子（-1）s（-1）来描述。测定了室温（T = 298 K）下etf反应的速率系数k1 =（1.90±0.19）× 10(-13) cm(3)分子（-1）s（-1）。用从头算的CBS-QB3和G4方法对OH + CH3C(O)F反应的微观机理进行了理论研究。利用变分过渡态理论，在从头算数据的基础上，得到了OH + CH3C(O)F反应速率系数随温度的变化规律。计算的速率系数与实验数据吻合较好。结果表明，该反应主要通过h键预反应配合物的间接吸氢机制进行，形成H2O和CH2CFO自由基的新生产物。在低于500 K的温度下，速率系数的非arrhenius行为归因于平面内吸氢动力瓶颈的显著隧穿效应。由于反应路线上存在明显的障碍，通过加成/消除机制生产FC(O)OH + CH3几乎没有竞争性。在248nm波长下，利用单束激光对AcF进行光化学实验。发现CH3C(O)F的总光解量子产率显著小于单位；在主要的光化学过程中，C-C键的裂解作用远远大于co -消除作用。与脂肪族羰基相比，AcF的吸收光谱显示出强烈的蓝移。讨论了这些结果对大气化学的影响。
The direct reaction kinetic method of low pressure fast discharge flow (DF) with resonance fluorescence monitoring of OH (RF) has been applied to determine rate coefficients for the overall reactions OH + C2H5F (EtF) (1) and OH + CH3C(O)F (AcF) (2). Acetyl fluoride reacts slowly with the hydroxyl radical, the rate coefficient at laboratory temperature is k2(300 K) = (0.74 ± 0.05) × 10(-14) cm(3) molecule(-1) s(-1) (given with 2σ statistical uncertainty). The temperature dependence of the reaction does not obey the Arrhenius law and it is described well by the two-exponential rate expression of k2(300-410 K) = 3.60 × 10(-3) exp(-10500/T) + 1.56 × 10(-13) exp(-910/T) cm(3) molecule(-1) s(-1). The rate coefficient of k1 = (1.90 ± 0.19) × 10(-13) cm(3) molecule(-1) s(-1) has been determined for the EtF-reaction at room temperature (T = 298 K). Microscopic mechanisms for the OH + CH3C(O)F reaction have also been studied theoretically using the ab initio CBS-QB3 and G4 methods. Variational transition state theory was employed to obtain rate coefficients for the OH + CH3C(O)F reaction as a function of temperature on the basis of the ab initio data. The calculated rate coefficients are in good agreement with the experimental data. It is revealed that the reaction takes place predominantly via the indirect H-abstraction mechanism involving H-bonded prereactive complexes and forming the nascent products of H2O and the CH2CFO radical. The non-Arrhenius behavior of the rate coefficient at temperatures below 500 K is ascribed to the significant tunneling effect of the in-the-plane H-abstraction dynamic bottleneck. The production of FC(O)OH + CH3 via the addition/elimination mechanism is hardly competitive due to the significant barriers along the reaction routes. Photochemical experiments of AcF were performed at 248 nm by using exciplex lasers. The total photodissociation quantum yield for CH3C(O)F has been found significantly less than unity; among the primary photochemical processes, C-C bond cleavage is by far dominating compared with CO-elimination. The absorption spectrum of AcF has also been determined by displaying a strong blue shift compared with the spectra of aliphatic carbonyls. Consequences of the results on atmospheric chemistry have been discussed.