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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Effect of Microhydration on Dissociation of Trifluoroacetic Acid
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Effect of Microhydration on Dissociation of Trifluoroacetic Acid

机译：微水化对三氟乙酸解离的影响

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First-principle-based electronic structure calculations were carried out on microhydrated trifluoroacetic acid clusters (CF_3COOH, tfa) to understand its molecular level interaction with water and subsequent ionic dissociation to form CF_3COO~- ion. From several geometrical inputs, the global minimum energy structure of hydrated cluster, tfa·nH_2O (n = 1-7), was obtained adopting dispersion-corrected density functional, namely, ωB97X-D, and a set of correlated atomic basis function, aug-cc-pVDZ. It was predicted that tfa requires at least six H_2O molecules to dissociate. Energy parameters of these hydrated clusters were improved by applying MP2 as well as CCSD(T) methods. A linear variation was observed for calculated solvent stabilization energy profile with the number of solvent H_2O molecules present in the hydrated cluster. However, the calculated interaction energy profile showed the characteristic feature indicating the formation of contact ion-pair on the addition of six H_2O molecules to tfa. On the basis of energy decomposition analysis, it was observed that the major interaction between tfa and H_2O molecules was of electrostatic nature. On successive addition of water molecules, the electrostatic component of the interaction between solute and solvent molecules depicted a sudden increase when moving from penta- to hexahydrated cluster. This observed nature of energy profile coincided with the formation of hydronium ion in the case of hexahydrated cluster. The formation of H_3O~+ was manifested in simulated IR spectra of tfa·6H_2O and tfa·7H_2O clusters. A large red shift in IR peak positions corresponding to O-H stretching of tfa was predicted on microhydration.
机译：对微水合三氟乙酸簇（CF_3COOH，tfa）进行基于第一原理的电子结构计算，以了解其与水的分子水平相互作用以及随后的离子离解形成CF_3COO〜-离子。从几个几何输入中，采用弥散校正的密度泛函ωB97X-D和一组相关的原子基础函数aug，得到了水合团簇的全局最小能量结构tfa·nH_2O（n = 1-7）。 -cc-pVDZ。据预测，tfa需要至少六个H_2O分子解离。通过应用MP2和CCSD（T）方法可以改善这些水合簇的能量参数。对于水合簇中存在的溶剂H_2O分子的数量，观察到的计算得出的溶剂稳定能曲线具有线性变化。然而，计算出的相互作用能谱显示出特征性特征，表明在向tfa中添加六个H_2O分子时形成了接触离子对。在能量分解分析的基础上，观察到tfa与H_2O分子之间的主要相互作用是静电性质。随着水分子的不断添加，溶质与溶剂分子之间相互作用的静电成分从五水簇转变为六水合物簇时突然增加。在六水合簇的情况下，这种观察到的能量分布的性质与水合氢离子的形成相吻合。在tfa·6H_2O和tfa·7H_2O团簇的模拟红外光谱中可以看出H_3O〜+的形成。在微水合作用上，预测了与tfa的O-H拉伸相对应的IR峰位置会出现大的红移。

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