Reactions associated with ionization in water: a direct ab initio dynamics study of ionization in (H2O)17.
Reactions associated with ionization in water: a direct ab initio dynamics study of ionization in (H2O)17.
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DOI：
10.1063/1.2194904
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发表时间：
2006-04
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影响因子：
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通讯作者：
Ayako Furuhama;Michel Dupuis;Kimihiko Hirao
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文献类型：
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作者：
Ayako Furuhama;Michel Dupuis;Kimihiko Hirao
用准经典从头算方法模拟了(H(2)O)(17)团簇中的电离动力学，得到了水溶液模型中电离引起的基本过程和能量再分配的详细图像.从模拟中可以观察到的一般特征如下：(I)在电离后的100秒内，可以看到一个或多个质子从“电离分子”转移到邻近的分子或更远的地方，形成一个离子离子和一个羟基自由基；(Ii)靠近电离水分子的两个水分子在反应中发挥重要作用，我们称之为“反应性三聚体”。反应时间由电离水分子与这两个相邻分子的相遇来控制，这发生在电离后10到50 fS之间的任何时间。电离分子与邻近分子之间的接近距离确实最好地显示了质子转移的时间特性，从而最好地反映了氢离子和羟基自由基形成的时间特性。这些发现与较小的环状星团的结果是一致的，尽管质子转移的动力学在较大的星系团中表现出比在小的环状星系团中更多的变化。我们对(H(2O)O)(17)体系中的动能使用了一种划分方案，该方案区分了反应性三聚体和周围的“介质”。对模拟的分析表明，电离事件发生后，周围介质的动能立即显著增加，这是介质局部加热的表现。动能的增加与周围介质的重组是一致的，在很短的时间内，由水阳离子静电强迫，在较长的时间内，由离子形成。
Quasiclassical ab initio simulations of the ionization dynamics in a (H(2)O)(17) cluster, the first water cluster that includes a fourfold coordinated (internally solvated) water molecule, have been carried out to obtain a detailed picture of the elementary processes and energy redistribution induced by ionization in a model of aqueous water. General features observable from the simulations are the following: (i) well within 100 fs following the ionization, one or more proton transfers are seen to take place from the "ionized molecule" to neighboring molecules and beyond, forming a hydronium ion and a hydroxyl radical; (ii) two water molecules close to the ionized water molecule play an important role in the reaction, in what we term a "reactive trimer." The reaction time is gated by the encounter of the ionized water molecule with these two neighboring molecules, and this occurs anytime between 10 and 50 fs after the ionization. The distances of approach between the ionized molecule and the neighboring molecules indeed display best the time characteristics of the transfer of a proton, and thus of the formation of a hydronium ion and a OH radical. These findings are consistent with those for smaller cyclic clusters, albeit the dynamics of the proton transfer displays more varieties in the larger cluster than in the small cyclic clusters. We used a partitioning scheme for the kinetic energy in the (H(2)O)(17) system that distinguishes between the reactive trimer and the surrounding "medium." The analysis of the simulations indicates that the kinetic energy of the surrounding medium increases markedly right after the event of ionization, a manifestation of the local heating of the medium. The increase in kinetic energy is consistent with a reorganization of the surrounding medium, electrostatically forced in a very short time by the water cation and in a longer time by the formation of the hydronium ion.