Song Xinli, Zügner Gábor L, Farkas Mária, Illés Ádám, Sarzyński Dariusz, Rozgonyi Tamás, Wang Baoshan, Dóbé Sándor
†College of Chemistry and Molecular Sciences, Wuhan University, Wuhan 430072, People's Republic of China.
‡Institute of Materials and Environmental Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences, 1117 Budapest, Hungary.
J Phys Chem A. 2015 Jul 16;119(28):7753-65. doi: 10.1021/acs.jpca.5b01069. Epub 2015 Apr 23.
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.
采用低压快速放电流动（DF）与OH的共振荧光监测（RF）的直接反应动力学方法，来测定总反应OH + C2H5F（EtF）（1）和OH + CH3C（O）F（AcF）（2）的速率系数。乙酰氟与羟基自由基反应缓慢，实验室温度下的速率系数为k2(300 K) = (0.74 ± 0.05) × 10(-14) cm(3) molecule(-1) s(-1)（给出2σ统计不确定度）。该反应的温度依赖性不遵循阿伦尼乌斯定律，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) molecule(-1) s(-1)能很好地描述。已测定室温（T = 298 K）下EtF反应的速率系数k1 = (1.90 ± 0.19) × 10(-13) cm(3) molecule(-1) s(-1)。还使用从头算CBS - QB3和G4方法从理论上研究了OH + CH3C（O）F反应的微观机制。基于从头算数据，采用变分过渡态理论获得OH + CH3C（O）F反应速率系数随温度的变化。计算得到的速率系数与实验数据吻合良好。结果表明，该反应主要通过涉及氢键预反应复合物的间接氢提取机制进行，并生成H2O和CH2CFO自由基的初生产物。低于500 K时速率系数的非阿伦尼乌斯行为归因于面内氢提取动态瓶颈的显著隧穿效应。由于反应路径上存在显著势垒，通过加成/消除机制生成FC（O）OH + CH3的反应几乎没有竞争力。使用激基复合物激光器在248 nm下进行了AcF的光化学实验。已发现CH3C（O）F的总光解离量子产率远小于1；在主要光化学过程中，与CO消除相比，C - C键断裂占主导地位。还通过与脂肪族羰基化合物的光谱相比显示出强烈的蓝移，测定了AcF的吸收光谱。讨论了这些结果对大气化学的影响。
