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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Kinetics and Mechanism of the Reversible Dissociation of Ammonium Carbamate: Involvement of Carbamic Acid
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Kinetics and Mechanism of the Reversible Dissociation of Ammonium Carbamate: Involvement of Carbamic Acid

机译：氨基甲酸铵可逆离解的动力学和机理：氨基甲酸的参与

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摘要

The kinetics of the reversible decomposition of ammonium carbamate, HN_4CO_2NH_2 (AC), into NH_3 (A) and CO_2 (C) has been studied between 278 and 312 K by recording the time dependence of the total pressure above an AC sample that, after being previously evacuated, is exposed to the headspace of an isoteniscope. At early times (＜1 s), the data show an inflection, which is enhanced in first derivative transformations. Three mechanisms are discussed, each containing sic rate constants. Two assume the presence of gas phase carbamic acid (CA) as an intermediate. These mechanisms are explored further through ab initio computational studies of CA. These results indicate that gas phase CA is a very stable species. No evidence could be found for its presence from Fourier transform IR spectra of the equilibrium vapor above AC. The mechanism that we suggest involves the reversible decomposition of AC into surface-bound CA, A, and C molecules, with the latter tow reversibly desorbing from the surface. The experimental kinetic data are consistent with all three mechanisms. The rate data do not contain sufficient information to allow all rate constants to be uniquely determined. Simulation studies are used to demonstrate consistency of the mechanisms with the data.
机译：氨基甲酸铵HN_4CO_2NH_2（AC）可逆分解为NH_3（A）和CO_2（C）的动力学已在278和312 K之间进行了研究，方法是记录AC样品上方总压力随时间变化的时间依赖性。先前抽成真空的容器暴露于等渗镜的顶部空间。在早期（＜1 s），数据显示出拐点，在一阶导数变换中得到了增强。讨论了三种机制，每个机制都包含sic速率常数。两个假设存在气相氨基甲酸（CA）作为中间体。通过对CA进行从头计算研究，可以进一步探索这些机制。这些结果表明气相CA是非常稳定的物质。从AC上方的平衡蒸气的傅里叶变换IR光谱中找不到其存在的证据。我们建议的机制涉及将AC可逆分解为表面结合的CA，A和C分子，而后者从表面可逆地解吸。实验动力学数据与所有三种机理一致。速率数据没有包含足够的信息以允许唯一确定所有速率常数。仿真研究用于证明机制与数据的一致性。

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