| Summary: | 博士 === 輔仁大學 === 化學系 === 102 === In this thesis, several kinds of the hydrated anion clusters are investigated using ab-initio and BOMD with density functional theory methods. The systems studied include X2-(H2O) [X = O, F] clusters and the charge-transfer-to-solvent (CTTS) excited states in I-(H2O)4 clusters. Studies of these systems help to obtain a deeper understanding of the hydration phenomena from a molecular viewpoint.
By investigating the relaxed potential energy surfaces (RPES) of X2-(H2O) [X = O, F] along the interatomic distance of X2-, a critical distance, rc, is found to separate the Cs and C2v conformers in the RPESs of not only O2-(H2O) but also F2-(H2O) clusters. The Cs conformer prevails in a small r(X1-X2) < rc, while the C2v conformer dominates at distances larger than rc. The critical distances are ~1.37 Å and ~1.71 Å for O2-(H2O) and F2-(H2O), respectively. In addition, from the energetic analysis of each energy component of the total energy for X2-(H2O), the electron correlation energy is determined to be crucial for correctly predicting the water binding motif to X2-. Besides, in the discussion of the radius of gyration of the excess electron on the binding motifs, we define the component of the radius of gyration of the excess electron in the X2 bond axis direction, δx. The results suggest that a critical value of δx, δx,m ~ 0.84 Å, to determine the water binding motif. This value is independent of the identity of X2. With δx,m as the threshold, the Cs binding motif is formed for a compact excess electron and the C2v binding motif prevails for a diffuse one.
On the other hand, in our CTTS excited state molecular dynamic studies in I-(H2O)4 clusters, the simulations are performed starting from C1’ and C1’-like initial configurations. The C1’ configuration, different from the previous studies, is the second low-lying energy conformer. The main reason for choosing the C1’ initial configuration is due to its dangling water molecule containing. We found that the relaxation dynamics starting from the C1’ initial configuration are very similar to those reported for larger [I-(H2O)n]* clusters with dangling water molecules, showing that they have similar intrinsic CTTS dynamic behaviors. However, the relaxation for the C1’ [I-(H2O)4]* cluster is faster in time, presumably due to a higher strain of the three-member ring in the cluster. In addition, the iodine effects on the CTTS relaxation dynamics are also discussed by the comparison of the differences between the VDEs of the excited electron in I-(H2O)4 clusters and those of the excess electron in the corresponding e-(H2O)4 clusters, δVDE, and by the analyses of the radius of gyration of the excess electron. The results of our CTTS dynamic simulations suggest that the iodine atom exerts a dual repulsion-and-attraction force on the photoexcited electron depending on the ratio of the iodine-electron distance to the radius of gyration of the excess electron of the corresponding water cluster anion: d/r. In the region of d/r < ~0.8, the iodine exerts an exclusion-repulsion force on the excited electron. Conversely, for values of d/r > ~1.0, the iodine can exert an attractive force on the excited electron due to the induced dipole moment of iodine. Finally, the attractive force is expected to fade out at very large distances because the iodine-electron distance is too great for any interaction to occur between them, and the relaxed cluster turns into a water cluster anion.
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