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• 作者：Xinli Song ; G谩bor L. Z眉gner ; M谩ria Farkas ; 脕d谩m Ill茅s ; Dariusz Sarzy艅ski ; Tam谩s Rozgonyi ; Baoshan Wang ; S谩ndor D贸b茅
• 刊名：Journal of Physical Chemistry A
• 出版年：2015
• 出版时间：July 16, 2015
• 年：2015
• 卷：119
• 期：28
• 页码：7753-7765
• 全文大小：559K
• ISSN：1520-5215

文摘

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 卤 0.05) 脳 10^鈥?4 cm³ molecule^鈥? s^鈥? (given with 2蟽 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鈥?10 K) = 3.60 脳 10^鈥?鈥痚xp(鈭?0500/T) + 1.56 脳 10^鈥?3鈥痚xp(鈭?10/T) cm³ molecule^鈥? s^鈥?. The rate coefficient of k₁ = (1.90 卤 0.19) 脳 10^鈥?3 cm³ molecule^鈥? s^鈥? 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鈥揅 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.