Pekkanen Timo T, Valkai László, Joshi Satya P, Lendvay György, Heinonen Petri, Timonen Raimo S, Eskola Arkke J
Department of Chemistry, University of Helsinki, P. O. Box 55 (A.I. Virtasen Aukio 1), 00014 Helsinki, Finland.
Institute of Materials and Environmental Chemistry, Research Centre for Natural Sciences, Magyar Tudósok Krt. 2, Budapest H-1117, Hungary.
Faraday Discuss. 2022 Oct 21;238(0):619-644. doi: 10.1039/d2fd00031h.
We have used laser-photolysis-photoionization mass spectrometry, quantum chemical calculations, and master equation simulations to investigate the kinetics of the reaction between (/)-pent-3-en-2-yl a resonance-stabilised hydrocarbon radical, and molecular oxygen. The time-resolved experiments were performed over a wide temperature range (240-750 K) at relatively low pressures (0.4-7 Torr) under pseudo-first-order conditions (excess [O]). Helium bath gas was used in most experiments, but nitrogen was employed in a few measurements to investigate the effect of a heavier collider on the kinetics of the studied reaction. The experimental traces were directly used to optimise parameters in the master equation model using the recently implemented trace fitting feature in the MESMER program. At low temperatures ( < 300 K), the reaction proceeds by barrierless recombination reactions to form peroxyl adducts, and the radical traces are single-exponential. Between 326 K and 376 K, equilibration between the reactants and the peroxyl adducts is observed, and the radical traces are multi-exponential. Interestingly, at temperatures above 500 K, single-exponential decays were again observed, although the reaction is much slower than at low temperatures. The master equation simulations revealed that at both low and high temperatures, the radical decay rate is governed by a single eigenvalue. At low temperatures, this eigenvalue corresponds to recombination reactions, and at high temperatures to the phenomenological formation of bimolecular products. Between low and high temperatures (the exact temperature thresholds depend on [O]), there is a region of avoided crossing in which the rate coefficient "jumps" from one eigencurve to the other. Although chemically significant eigenvalues are not well separated from internal energy relaxation eigenvalues at elevated temperatures (600 K at 0.01 bar, 850 K at 100 bar), we observed that many of the Bartis-Widom rate coefficients produced by the master equation model were valid up to 1500 K. Our simulations predict that the most important reaction channel at high temperatures is the formation of (/)-penta-1,3-diene and hydroperoxyl. The experimentally constrained master equation model was used to simulate the title reaction over a wide range of conditions. To facilitate the use of our results in autoignition and combustion models, modified Arrhenius representations are given for the most important reaction channels.
我们利用激光光解-光电离质谱、量子化学计算和主方程模拟，研究了（/）-戊-3-烯-2-基（一种共振稳定的烃基）与分子氧之间反应的动力学。时间分辨实验在较宽的温度范围（240 - 750 K）、相对较低的压力（0.4 - 7 Torr）下，在准一级条件（过量[O]）下进行。大多数实验使用氦气作为浴气，但少数测量中使用氮气，以研究较重的碰撞体对所研究反应动力学的影响。实验轨迹直接用于利用MESMER程序中最近实现的轨迹拟合功能来优化主方程模型中的参数。在低温（< 300 K）下，反应通过无势垒的复合反应进行，形成过氧加合物，自由基轨迹为单指数形式。在326 K至376 K之间，观察到反应物与过氧加合物之间达到平衡，自由基轨迹为多指数形式。有趣的是，在高于500 K的温度下，再次观察到单指数衰减，尽管反应比低温时慢得多。主方程模拟表明，在低温和高温下，自由基衰减速率均由单个本征值控制。在低温下，该本征值对应于复合反应，在高温下对应于双分子产物的唯象形成。在低温和高温之间（确切的温度阈值取决于[O]），存在一个避免交叉区域，在此区域速率系数从一条本征曲线“跳跃”到另一条。尽管在高温（0.01 bar时为600 K，100 bar时为850 K）下化学上有意义的本征值与内能弛豫本征值没有很好地分离，但我们观察到主方程模型产生的许多巴蒂斯-维登速率系数在高达1500 K时都是有效的。我们的模拟预测，高温下最重要的反应通道是形成（/）-戊-1,3-二烯和氢过氧基。经实验约束的主方程模型用于在广泛的条件下模拟该标题反应。为便于在自燃和燃烧模型中使用我们的结果，给出了最重要反应通道的修正阿伦尼乌斯表达式。
