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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Coexistence of Neutral and Ion-Pair Clusters of Hydrated Sulfuric Acid H_2SO_4(H_2O)_n(n=1-5)-A Molecular Orbital Study
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Coexistence of Neutral and Ion-Pair Clusters of Hydrated Sulfuric Acid H_2SO_4(H_2O)_n(n=1-5)-A Molecular Orbital Study

机译：水合硫酸H_2SO_4（H_2O）_n（n = 1-5）中性和离子对簇的共存-分子轨道研究

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摘要

Various isomeric structures of the hydrated clusters of sulfuric acid, H_2SO_4(H_2O)_n(n=1-5), are examined using a density functional molecular orbital method. Due to the small energy difference between trans and cis conformations about two OH groups of sulfuric acid, there are three types of isomeric forms of the hydrated clusters of sulfuric acid which involve the proton nontransferred trans confomer, the proton transferred trans conformer, and the proton nontransferred cis conformer of sulfuric acid. In the case of transoid H_2SO_4, the proton transferred ion-pair structures become more stable than the proton nontransferred structures as the number of water molecules increases. The hydrated clusters of the cis conformation remain neutral Hydrogenbonded structures even if the number of water molecules increases. All stable clusters tend to form multicyclic structures. While both protons of sulfuric acid participate in cyclic hydrogen bonding in th neutral structures, the OH group of HSO_4~_ in the ion-pair structures remains dangling because the counterion H_3O~+ prefers to make strong hydrogen bonds with water molecules and/or the HSO_4~- moiety. The energy difference between the most stable structures of proton transferred and proton nontransferred isomers is found to be less than 1 kcal/mol in the case of n=3 and 4 clusters. The ion-pair structure of HSO_4~-H_3O~+(H_2O)_4 becomes 2 kcal/mol more stable than the hydrogen-bonded neutral cluster H_2SO_4(H_2O)_5 in the case of n=5. Analyzing the interaction energies, many-body interaction is shown to be essential to describe the stablity between neutral and ionic clusters owing to the difference of charge flow on the neutral and ion-pair structures in multi-cyclic hydrogen bonding. The calculated IR spectra of stable isomers of H_2SO_4(H_2O)_n clusters clearly demonstrate the significant red-shift of OH stretching of sulfuric acid and hydrogen-bonded OH stretching of water molecules as the number of cluster size increases. The IR spectra of the OH stretching of hydrated sulfuric acid ar predicted t appear in three regions, hydrogen-bonded OH stretching of H_3O~+(2500 approx 2800 cm~(_1), hydrogen-bonded OH stretching of water molecules (3100 approx 3500 cm~(-1)), and nonhydrogen-bonded OH stretching of water molecules (3800 approx 3900 cm~(-1)).
机译：使用密度泛函分子轨道方法研究了硫酸水合簇H_2SO_4（H_2O）_n（n = 1-5）的各种异构结构。由于两个硫酸基团的反式和顺式构象之间的能量差很小，因此，硫酸水合簇的三种异构形式包括质子非转移的反式共聚体，质子转移的反式构象体和质子未转移的顺式构象硫酸。在Transoid H_2SO_4的情况下，随着水分子数量的增加，质子转移的离子对结构比质子非转移的结构更稳定。即使水分子的数量增加，顺式构象的水合簇仍保持中性的氢键结构。所有稳定的簇倾向于形成多环结构。虽然两个硫酸质子都参与中性结构中的环状氢键结合，但离子对结构中HSO_4〜_的OH基仍然悬空，因为抗衡离子H_3O〜+倾向于与水分子和/或氢键形成强氢键。 HSO 4-部分。在n = 3和4团簇的情况下，发现质子转移和非质子转移的最稳定结构之间的能量差小于1 kcal / mol。在n ＝ 5的情况下，HSO_4〜-H_3O〜+（H_2O）_4的离子对结构比氢键合的中性簇H_2SO_4（H_2O）_5稳定2 kcal / mol。分析相互作用能，表明多体相互作用对于描述中性和离子簇之间的稳定性至关重要，这是由于在多环氢键作用下中性和离子对结构上的电荷流不同。 H_2SO_4（H_2O）_n团簇的稳定异构体的红外光谱计算结果清楚地表明，随着团簇尺寸的增加，硫酸的OH伸张和水分子的氢键OH伸张明显红移。预测t的水合硫酸OH拉伸的红外光谱出现在三个区域，H_3O〜+（2500约2800 cm〜（_1）的氢键OH拉伸，水分子的氢键OH拉伸（3100约3500） cm〜（-1））和水分子的非氢键OH拉伸（3800约3900 cm〜（-1））。

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