Tachikawa Hiroto
Division of Materials Chemistry, Graduate School of Engineering, Hokkaido University, Sapporo 060-8628, Japan.
Phys Chem Chem Phys. 2008 Apr 28;10(16):2200-6. doi: 10.1039/b718017a. Epub 2008 Mar 3.
Dissociative electron capture dynamics of halocarbon absorbed on water cluster anion, caused by internal electron transfer from the water trimer anion to the halocarbon, have been investigated by means of the direct density functional theory (DFT)-molecular dynamics (MD) method. The CF(2)Cl(2) molecule and a water trimer anion e(-)(H(2)O)(3) were used as a halocarbon and a trapped electron, respectively. First, the structure of trapped electron state, expressed by e(-)(H(2)O)(3)-CF(2)Cl(2), was fully optimized. The excess electron was trapped by a dipole moment of water trimer. Next, initial geometries were randomly generated around the equilibrium point of the trapped electron state, and then trajectories were run. The direct DFT-MD calculations showed that the spin density distribution of excess electron is gradually changed from the water cluster (trapped electron state) to CF(2)Cl(2) as a function of time. Immediately, the Cl(-) ion was dissociated from CF(2)Cl(2)(-) adsorbed on the water cluster. The reaction was schematically expressed by e(-)(H(2)O)(3)-CF(2)Cl(2)-->(H(2)O)(3)-->-CF(2)CL(2) --> (H(2O)(3) + CF(2)CL + CI(-) (I) where (H(2)O)(3)-CF(2)Cl(2) indicates a transient intermediate state in which the excess electron is widely distributed on both the water cluster and CF(2)Cl(2). The mechanism of the electron capture of halocarbon from the trapped electron in water ice was discussed on the basis of the theoretical results. Also, the dynamics feature was compared with those of the direct electron capture reactions of CF(2)Cl(2) and CF(2)Cl(2)-(H(2)O)(3), i.e. e(-) + CF(2)Cl(2), and e(-) + CF(2)Cl(2)-(H(2)O)(3), investigated in our previous paper [Tachikawa and Abe, J. Chem. Phys., 2007, 126, 194310].
通过直接密度泛函理论（DFT）-分子动力学（MD）方法，研究了水簇阴离子上吸附的卤代烃的解离电子俘获动力学，该动力学是由水三聚体阴离子向卤代烃的内部电子转移引起的。分别使用CF(2)Cl(2)分子和水三聚体阴离子e(-)(H(2)O)(3)作为卤代烃和俘获电子。首先，对由e(-)(H(2)O)(3)-CF(2)Cl(2)表示的俘获电子态的结构进行了完全优化。多余的电子被水三聚体的偶极矩俘获。接下来，在俘获电子态的平衡点周围随机生成初始几何结构，然后运行轨迹。直接DFT-MD计算表明，多余电子的自旋密度分布随时间从水簇（俘获电子态）逐渐变化到CF(2)Cl(2)。紧接着，Cl(-)离子从吸附在水簇上的CF(2)Cl(2)(-)上解离。该反应示意性地表示为e(-)(H(2)O)(3)-CF(2)Cl(2)-->(H(2)O)(3)-->-CF(2)CL(2) --> (H(2O)(3) + CF(2)CL + CI(-) （I），其中(H(2)O)(3)-CF(2)Cl(2)表示一种瞬态中间态，其中多余电子广泛分布在水簇和CF(2)Cl(2)上。基于理论结果讨论了在水冰中卤代烃从俘获电子处俘获电子的机制。此外，还将动力学特征与我们之前论文[Tachikawa和Abe，J. Chem. Phys.，2007，126，194310]中研究过的CF(2)Cl(2)和CF(2)Cl(2)-(H(2)O)(3)的直接电子俘获反应的动力学特征进行了比较，即e(-) + CF(2)Cl(2)和e(-) + CF(2)Cl(2)-(H(2)O)(3)。
