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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Reactions of Atomic Hydrogen with Formic Acid and Carbon Monoxide in Solid Parahydrogen II: Deuterated Reaction Studies
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Reactions of Atomic Hydrogen with Formic Acid and Carbon Monoxide in Solid Parahydrogen II: Deuterated Reaction Studies

机译：固体对氢中原子氢与甲酸和一氧化碳的反应II：氘代反应研究

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摘要

It is difficult to determine whether the measured rate constant for reaction of atomic hydrogen with formic acid reported in Part 1 reflects the H atom quantum diffusion rate or the rate constant for the tunneling reaction step. In Part 2 of this series, we present kinetic studies of the postphotolysis H atom reactions with deuterated formic acid (DCOOD) to address this ambiguity. Short duration 193 nm in situ photolysis of DCOOD trapped in solid parahydrogen results in partial depletion of the DCOOD precursor and photoproduction of primarily CO, CO_2, DOCO, HCO and mobile H atoms. At 1.9 K we observe post-irradiation growth in the concentrations of DOCO and HCO that can be explained by H atom tunneling reactions with DCOOD and CO, respectively. Conducting experiments with different deuterium isotopomers of formic acid (DCOOD, DCOOH, HCOOD and HCOOH) provides strong circumstantial evidence the reaction involves H atom abstraction from the alkyl group of formic acid. Further, the anomalous temperature dependence measured for the H + HCOOH reaction in Part 1 is also observed for the analogous reactions with deuterated formic acid. The rate constants extracted for H atom reactions with DCOOD and HCOOH are equivalent to within experimental uncertainty. This lack of a kinetic isotope effect in the measured rate constant is interpreted as evidence the reactions are diffusion limited; the measured rate constant reflects the H atom diffusion rate and not the tunneling reaction rate. Whether or not H atom reactions with chemical species in solid parahydrogen are diffusion limited is one of the outstanding questions in this field, and this work makes significant strides toward showing the reaction kinetics with formic acid are diffusion limited.
机译：很难确定在第1部分中报道的测得的氢原子与甲酸反应的速率常数是否反映了H原子的量子扩散速率或隧穿反应步骤的速率常数。在本系列的第2部分中，我们介绍了用氘代甲酸（DCOOD）进行光解后H原子反应的动力学研究，以解决这种歧义。固态对氢中捕获的DCOOD的短时193 nm原位光解导致DCOOD前体的部分耗竭并主要产生CO，CO_2，DOCO，HCO和可移动的H原子。在1.9 K时，我们观察到辐照后DOCO和HCO浓度的增长，这可以分别由H原子与DCOOD和CO的隧穿反应来解释。用甲酸的不同氘同位素异构体（DCOOD，DCOOH，HCOOD和HCOOH）进行实验提供了强有力的环境证据，表明该反应涉及从甲酸烷基中提取H原子。此外，对于与氘代甲酸的类似反应，在第1部分中对H + HCOOH反应测得的反常温度依赖性也被观察到。与DCOOD和HCOOH的H原子反应提取的速率常数等于实验不确定性之内。在测得的速率常数中缺乏动力学同位素效应，可以解释为反应受限。测得的速率常数反映了H原子的扩散速率，而不是隧穿反应速率。固态对氢中与化学物质发生的H原子反应是否受到扩散限制是该领域的突出问题之一，这项工作在显示与甲酸的反应动力学受到扩散限制方面取得了重大进展。

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