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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Rate Constants and Product Branching Fractions for the Reactions of H_3O~+ and NO~+ with C_2-C_(12) Alkanes
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Rate Constants and Product Branching Fractions for the Reactions of H_3O~+ and NO~+ with C_2-C_(12) Alkanes

机译：H_3O〜+和NO〜+与C_2-C_（12）烷烃反应的速率常数和产物分支分数

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摘要

Gas-phase ion molecule reactions of H_3O~+ and NO~+ with a number of C_2-C_(12) alkanes have been studied using a variable temperature-selected ion flow tube instrument. Reaction rate constants and product branching fractions were measured at 300 K, and temperature dependences of the rate constants and product branching fractions for reactions of C_7 and C_8 alkanes were examined from 300 to 500 K. The threshold size for H_3O~+ reaction occurs at hexane, with the reaction rate constants increasing steadily with alkane size. Association is the predominant reaction channel at 300 K for C_3-C_(12) alkanes, although these products thermally dissociate back into initial reactants between 300 and 400 K. The proton-transfer reaction channel is expected to be exothermic for large alkanes; however, this reaction channel does not proceed at the collision rate, nor are any direct proton-transfer product ions observed. The presence of smaller alkyl product ions suggests proton-transfer product ions may dissociate into smaller alkyl fragment ions and neutral alkanes. The threshold size for NO~+ reaction with n-alkanes also occurs at hexane, and the reaction proceeds primarily via hydride transfer as previous experiments have indicated. However, a number of smaller product ions are also observed for the reactions of NO~+ with all n-alkanes larger than butane, with the branching fraction of the nonhydride transfer product ions increasing with increasing alkane size. Together with our previously reported results regarding the reactions of various atmospheric ions with octane isomers, the present results indicate that H_3O~+, NO~+, and O_2~+ are not suitable chemical ionization agents for analysis of hydrocarbon emissions.
机译：使用可变温度选择离子流管仪器研究了H_3O〜+和NO〜+与许多C_2-C_（12）烷烃的气相离子分子反应。在300 K下测量了反应速率常数和产物支化级分，并考察了C_7和C_8烷烃反应的速率常数和产物支化级分的温度依赖性（300-500 K）。H_3O〜+反应的阈值大小在己烷中发生，反应速率常数随烷烃尺寸的增加而稳定增加。缔合是C_3-C_（12）烷烃在300 K时的主要反应通道，尽管这些产物在300和400 K之间会热分解回初始反应物。对于大烷烃，质子转移反应通道预计会放热。然而，该反应通道没有以碰撞速率进行，也没有观察到任何直接的质子转移产物离子。较小的烷基产物离子的存在表明质子转移产物离子可能解离为较小的烷基碎片离子和中性烷烃。与正构烷烃发生NO〜+反应的阈值大小也在己烷中发生，并且反应主要通过氢化物转移进行，如先前的实验所示。然而，对于NO〜+与所有大于丁烷的正构烷烃的反应，也观察到许多较小的产物离子，随着烷烃尺寸的增加，非氢化物转移产物离子的支化率也随之增加。结合我们先前报道的有关各种大气离子与辛烷异构体反应的结果，目前的结果表明H_3O〜+，NO〜+和O_2〜+不是用于分析烃排放的合适化学电离剂。

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