Time-resolved measurements of OH and HO2 product formation in pulsed-photolytic chlorine atom initiated oxidation of neopentane
Time-resolved measurements of OH and HO2 product formation in pulsed-photolytic chlorine atom initiated oxidation of neopentane
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脉冲光解氯原子引发的新戊烷氧化过程中 OH 和 HO2 产物形成的时间分辨测量
DOI：
10.1039/b211452f
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发表时间：
2003
影响因子：
3.3
通讯作者：
C. Taatjes
中科院分区：
文献类型：
--
作者：
J. Desain;S. Klippenstein;C. Taatjes
在573~750K温度范围内，测量了脉冲光解氯引发的新戊烷(2，2-二甲基丙烷)氧化过程中新戊烷(2，2-二甲基丙烷)的时间分辨产物。氧化过程中的初始反应是由氯 + 新戊烷生成的新戊基自由基(R)与O2的反应。生成的新戊基过氧基(RO2)可以异构化为氢过氧烷基(QOOH)并解离。由于新戊基过氧基不能形成共轭的烯烃 + HO2，而1，1-二甲基环丙烷 + HO2的生成在能量上是不容易的，因此新戊烷氧化过程中HO2的产生归因于RO2或QOOH自由基的二次反应。在623K以上测得明显的HO2生成，且HO2的生成随着温度的升高而增加。在673K，HO2的生成量随着O2的增加而增加，这与QOOH + O2在该体系的链分支中所起的作用是一致的。通过与前人对正丙基与O2反应相似过程的含时主方程计算的比较，建立了一个简单的动力学模型。目前的实验结果需要包含几个化学活化反应的形式直接路径，特别是从R + O2直接生成OH。通过类比正丙基 + O2来估算这些直接组分是相当成功的。从RO2到QOOH的异构化被发现比先前提出的要大得多。提出了建立普遍适用的烷基自由基氧化理论模型的可能途径。
The time-resolved production of HO2 and OH has been measured in pulsed-photolytic Cl-initiated oxidation of neopentane (2,2-dimethylpropane) between 573 and 750 K. The initial reaction in the oxidation process is the reaction of the neopentyl radical (R), formed by Cl + neopentane, with O2. The neopentylperoxy radical (RO2) formed can then isomerize to a hydroperoxyalkyl radical (QOOH) and dissociate. The production of HO2 in the neopentane oxidation is attributed to secondary reaction of the RO2 or QOOH radicals, since the neopentylperoxy radical cannot form a conjugate alkene + HO2, and formation of 1,1-dimethylcyclopropane + HO2 is energetically inaccessible. Significant HO2 formation is measured above 623 K, and the formation of HO2 increases with increasing temperature. The overall amount of HO2 produced increases with increasing O2 at 673 K, consistent with the proposed role for QOOH + O2 in chain branching for this system. A simple kinetic model is constructed based on comparison with previous time-dependent master equation calculations of analogous processes in the reaction of n-propyl with O2. The present experimental results require inclusion of formally direct pathways for several chemical activation reactions, especially direct production of OH from R + O2. Estimation of these direct components by analogy with n-propyl + O2 is reasonably successful. The isomerization from RO2 to QOOH is found to be significantly larger than previously proposed. A possible course towards a generally applicable theoretically-based model for alkyl radical oxidation is suggested.