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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >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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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)

机译：HFC-161（C2H5F）大气降解中间体乙酰氟（CH3C（O）F）的OH反应动力学和光化学的实验和理论研究

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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 k(2)(300 K) = (0.74 +/- 0.05) x 10(-14) cm(3) molecule(-1) s(-1) (given with 2 sigma 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 k(2)(300-410 K) = 3.60 x 10(-3) exp(-10500/T) + 1.56 x 10(-13) exp(-910/T) cm(3) molecule(-1) s(-1). The rate coefficient of k(1) = (1.90 +/- 0.19) x 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.
机译：低压快速放电流（DF）的直接反应动力学方法与OH（RF）的共振荧光监测已用于确定OH + C2H5F（EtF）（1）和OH + CH3C（O）总体反应的速率系数F（AcF）（2）。乙酰氟与羟基自由基缓慢反应，在实验室温度下的速率系数为k（2）（300 K）=（0.74 +/- 0.05）x 10（-14）cm（3）分子（-1）s（- 1）（考虑到2 sigma统计不确定性）。反应的温度依赖性不符合阿伦尼乌斯定律，并且通过k（2）（300-410 K）= 3.60 x 10（-3）exp（-10500 / T）的二指数速率表达式可以很好地描述+ 1.56 x 10（-13）exp（-910 / T）cm（3）分子（-1）s（-1）。已确定室温下EtF反应的k（1）=（1.90 +/- 0.19）x 10（-13）cm（3）分子（-1）s（-1）的速率系数（T = 298 K）。 OH + CH3C（O）F反应的微观机理在理论上也使用了从头算CBS-QB3和G4的方法进行了研究。基于从头算数据，采用变分过渡态理论来获得OH + CH3C（O）F反应的速率系数随温度的变化。计算出的速率系数与实验数据吻合良好。结果表明，该反应主要通过间接的H吸收机理发生，该机理涉及与H键合的预反应复合物，并形成H2O和CH2CFO自由基的新生产物。速率系数在低于500 K的温度下的非阿伦尼乌斯行为归因于平面内H吸收动态瓶颈的显着隧穿效应。由于沿着反应途径的显着障碍，通过加成/消除机理生产FC（O）OH + CH3几乎没有竞争力。通过使用激基复合物激光器在248 nm处进行AcF的光化学实验。已发现CH3C（O）F的总光解离量子产率明显小于1。在主要的光化学过程中，与CO消除相比，C-C键的裂解占主导地位。与脂肪族羰基的光谱相比，AcF的吸收光谱也通过显示出强烈的蓝移来确定。讨论了结果对大气化学的影响。

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