HOx regeneration in the oxidation of isoprene III: theoretical study of the key isomerisation of the Z-δ-hydroxy-peroxy isoprene radicals.
HOx regeneration in the oxidation of isoprene III: theoretical study of the key isomerisation of the Z-δ-hydroxy-peroxy isoprene radicals.
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异戊二烯氧化中的 HOx 再生 III：Z-δ-羟基过氧异戊二烯自由基关键异构化的理论研究。
DOI：
10.1002/cphc.201000480
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发表时间：
2010
期刊：
影响因子：
--
通讯作者：
J. Peeters
中科院分区：
文献类型：
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作者：
T. Nguyen;L. Vereecken;J. Peeters
作为我们关于拟议的新的异戊二烯氧化机制的通信的续篇，该机制旨在使在异戊二烯丰富的地区观察到的意外的高OH和HO(2)水平合理化(J.Peters，T.L.Nguyen，L.Vereecken，Phys.化学。化学。太棒了。，11,5935)，我们在这里报道了来自异戊二烯的两个Z-δ-羟基过氧基的关键的1，6-H位移的详细的量子化学和统计动力学表征。在B3LYP/6-31+G(d，p)水平上计算了反应物自由基和过渡态的所有构象的几何构型、能量和振动频率，然后在CBS-QB3、IRCMax(CBS-QB3//B3LYP)和CBS-APNO等不同的较高水平上对最低构象的能量进行了修正。用多构象过渡态理论计算了较宽温度范围内的速率系数，用CBS-QB3//B3LYP IRC分析计算了势垒形状的WKB隧穿因子。在室温下，这些烯丙基稳定辅助反应的WKB隧穿因子约为25。在250-350K范围内，速率系数可用Arrhenius公式表示：对于Z-1-OH-4-OO(·)-异戊二烯自由基，K(T)=1.4×10(9)exp(-6380/T)S(-1)；对于Z-1-OH-4-OO(·)-异戊二烯，k(T)=0.72×10(9)exp(-5520/T)S(-1)。在常温下，利用S(-1)的1级k(1，6-H)，这些异构化反应可以在低和中等NO水平下与传统的过氧反应竞争甚至超过过氧反应。讨论了这些反应作为关键过程在新提出的OH再生异戊二烯氧化方案中的重要性。
As a sequel to our communication on a proposed new isoprene oxidation mechanism aiming to rationalize the unexpectedly high OH and HO(2) levels observed in isoprene-rich areas (J. Peeters, T. L. Nguyen, L. Vereecken, Phys. Chem. Chem. Phys. 2009, 11, 5935), we report herein the detailed quantum chemical and statistical kinetics characterization of the crucial 1,6-H shifts in the two Z-δ-hydroxy-peroxy radicals from isoprene. Geometries, energies and vibration frequencies of all conformers of the reactant radicals and transition states are computed at the B3LYP/6-31+G(d,p) level of theory and the energies of the lowest-lying conformers are then refined at various higher levels of theory, including CBS-QB3, IRCMax(CBS-QB3//B3LYP) and CBS-APNO. The rate coefficients over a wide temperature range are calculated using multi-conformer transition state theory with WKB tunneling factors evaluated for the barrier shape found by CBS-QB3//B3LYP IRC analyses. The WKB tunneling factors for these allyl-stabilisation-assisted reactions are about 25 at ambient temperatures. The rate coefficients can be represented by Arrhenius expressions over the 250-350 K range: k(T)=1.4×10(9) exp(-6380/T) s(-1) for the Z-1-OH-4-OO(·)-isoprene radical, and k(T)=0.72×10(9) exp(-5520/T) s(-1) for Z-1-OH-4-OO(·)-isoprene. With the k(1,6-H) of order 1 s(-1) at ambient temperatures, these isomerisations can compete with and even outrun the traditional peroxy reactions at low and moderate NO levels. The importance of these reactions as key processes in the newly proposed, OH-regenerating isoprene oxidation scheme is discussed.