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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Excited State of Iodide Anions in Water: A Comparison of the Electronic Structure in Clusters and in Bulk Solution
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Excited State of Iodide Anions in Water: A Comparison of the Electronic Structure in Clusters and in Bulk Solution

机译：水中碘化物阴离子的激发态：簇和体溶液中电子结构的比较

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摘要

A new computational approach for calculating charger-transfer-to-solvent (CTTS) states of anions in polar solvents is presented. This is applied to the prototypical aqueous iodide system when the anion is placed in the interior or at the gas-liquid interface of a bulk water solution or hydrated in small gas phase clusters. The experimental vertical detachment energies and CTTS transition energies are quantitatively reproduced without any adjustable parameters. The representative shapes of bulk CTTS wave functions are shown for the first time and compared with cluster excited states. The calculations start with an equilibrium classical molecular dynamics simulation of the solvated anion, allowing for an extended sampling of initial configurations. In the next step, ab initio calculations at the MP2 level employing an extended diffuse basis set are performed for the anionic ground and lowest triplet state, as well as for the corresponding neutral system. It is argued that due to the small singlet-triplet splitting, the triplet state is a good model for the experimental CTTS state. The present calculations on aqueous iodide ion are made computationally feasible by replacing all water molecules (or all waters except for the first solvation shell) by fractional point charges. It is concluded that the bulk wave function is mainly defined by the instantaneous location of voids in the first solvation shell, which arise due to thermal disorder in liquid water. The key ingredient to CTTS binding in the bulk is the long-range electrostatic field due to the preexisting polarization of water molecules by the ground state iodide ion. This is very different from the situation in small water clusters, where the CTTS state is an order of magnitude more fragile due to the lack of long-range polarization. Therefore, it is argued that the electronic structure of small halide clusters cannot be directly extrapolated to the bulk.
机译：提出了一种新的计算方法，用于计算极性溶剂中阴离子的电荷转移到溶剂（CTTS）状态。当将阴离子置于大体积水溶液的内部或气液界面或在小型气相簇中水合时，可将其应用于原型碘水溶液。在没有任何可调参数的情况下，定量地再现了实验的垂直脱离能和CTTS跃迁能。首次显示了体CTTS波函数的代表性形状，并将其与团簇激发态进行了比较。计算从溶剂化阴离子的平衡经典分子动力学模拟开始，从而可以扩展初始构型的采样。下一步，对阴离子基态和最低三重态以及相应的中性系统，使用扩展的扩散基集在MP2级别进行从头算。有人认为，由于单重态-三重态分裂较小，三重态是实验性CTTS状态的良好模型。通过用分数点电荷代替所有水分子（或除第一溶剂化壳之外的所有水），使碘化氢离子的当前计算在计算上可行。结论是，体波函数主要由第一溶剂化壳中空隙的瞬时位置决定，这些空隙是由于液态水中的热紊乱而产生的。大部分CTTS结合的关键成分是远程静电场，这是由于基态碘离子预先存在的水分子极化作用所致。这与小型水团簇中的情况非常不同，在小型水团簇中，由于缺乏远程极化，CTTS状态更加脆弱。因此，有人认为，小卤化物簇的电子结构不能直接外推到大部分。

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