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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Muonium Addition Reactions and Kinetic Isotope Effects in the Gas Phase: k(infinity) Rate Constants for Mu + C2H2
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Muonium Addition Reactions and Kinetic Isotope Effects in the Gas Phase: k(infinity) Rate Constants for Mu + C2H2

机译：气相中的加成反应和动力学同位素效应：Mu + C2H2的k（无穷大）速率常数

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摘要

The kinetics of the addition reaction of muonium (Mu) to acetylene have been studied in the gas phase at N-2 moderator pressures mainly from similar to 800 to 1000 Torr and over the temperature range from 168 to 446 K, but also down to 200 Torr at 168 K and over a much higher range of pressures, from 10 to 44 bar at 295 K, demonstrating pressure-independent rate constants, k(Mu)(T). Even at 200 Torr moderator pressure, the kinetics for Mu + C2H2 addition behave as if effectively in the high-pressure limit, giving k infinity = k(Mu) due to depolarization of the muon spin in the MuC(2)H(2) radical formed in the addition step. The rate constants k(Mu)(T) exhibit modest Arrhenius curvature over the range of measured temperatures. Comparisons with data and with calculations for the corresponding H(D) + C2H2 addition reactions reveal a much faster rate for the Mu reaction at the lowest temperatures, by 2 orders of magnitude, in accord with the propensity of Mu to undergo quantum tunneling. Moreover, isotopic atom exchange, which contributes in a major way to the analogous D atom reaction, forming C2HD + H, is expected to be unimportant in the case of Mu addition, a consequence of the much higher zero-point energy and hence weaker C-Mu bond that would form, meaning that the present report of the Mu + C2H2 reaction is effectively the only experimental study of kinetic isotope effects in the high-pressure limit for H-atom addition to acetylene.
机译：在气相中研究了of（Mu）与乙炔的加成反应动力学，主要是在N-2减速器压力下，压力从大约800至1000 Torr，在168至446 K的温度范围内，但也下降至200在168 K和更高的压力范围（295 K下从10 bar到44 bar）下的Torr，显示出与压力无关的速率常数k（Mu）（T）。即使在200 Torr减速器压力下，Mu + C2H2加成的动力学表现也好像在高压极限内一样有效，由于MuC（2）H（2）中的介子自旋去极化，因此k无穷大= k（Mu）。在加成步骤中形成的自由基。速率常数k（Mu）（T）在测得的温度范围内表现出适度的阿累尼乌斯曲率。与数据和相应的H（D）+ C2H2加成反应的计算比较表明，在最低温度下，Mu反应的速率要快2个数量级，这与Mu进行量子隧穿的倾向相符。此外，在添加Mu的情况下，同位素原子交换（对形成C2HD + H的类似D原子反应起主要作用）起主要作用，由于零点能量高得多，因此C弱，导致这种情况预计不重要将会形成-Mu键，这意味着Mu + C2H2反应的当前报告实际上是在高压原子中向乙炔中添加H原子的动力学同位素效应的唯一实验研究。

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