Studies On The Reactivity Of Hydrated Electron In Aqueous Solution By Ab Initio Molecular Dynamics Simulation

As the most fundamental chemical reagent as well as carriers of negative charge, widely experimental and theoretical efforts have focused on elucidating the structure and solvation dynamics of excess electron in a variety of systems. Such electrons exist mainly in three forms:solvent-bound valence anions, cavity-type solvated states, and diffuse states, depending on the medium’s electronic properties, heterogeneity, and degree of aggregation. On the basis of the previous reports, many simulations and experiments have been performed to characterize the role of excess electron in biological chemistry and solvent chemistry. As the fundamental chemistry reactant, excess electron in solvent could give rise to a series of chemical reaction and free radical reaction. We performed a series of work to interpret the reactivity of excess electron in solvent and obtained valuable results on these issues. The primary innovations are related as follows.1. Localization and time evolution dynamics of an excess electron in heterogeneous CO2-H2O systems.We present an ab initio molecular dynamics simulation study of an excess electron (EE) in the heterogeneous CO2-H2O system. Various information regarding structures, state, and dynamics of an excess electron in localization and time evolution processes in such heterogeneous CO2-H2O mixed media are acquired. Results indicate that bending vibration of CO2plays the major role in the EE localization, while water molecules only play an assisting role. Due to the hydration, CO2even can capture a hydrated electron from a solvated cavity. With strong attraction of CO2in the hydrated structures, an EE resides in the empty, low-lying π*orbital of CO2and changes the neutral, linear CO2molecule into a bent, polar CO2-anion surrounded by solvent water molecules, and the localization process takes only a few tens of femtoseconds. After EE trapping, the (?)OCO angle of the CC2-core oscillates in the range of127°～142°with a vibration period about48fs, and the corresponding vertical detachment energy is about4.0eV which indicates extreme stability of such an core-bound solvated EE in [CO2(H2O)n]-. Hydration mainly occurs on the O atoms of the CO2anion through forming the O…H-O hydrogen bond. Expect for the O……H-O interaction, a new C…H-O hydrogen bonding mode was also observed in the anionic clusters and CO2aqueous solution in which an O-H group of water molecule forms a hydrogen-bond with the C atom. Geometry optimizations of some of small CO2(?)(H2O)n (n=2-6) clusters have also evidenced the existence of the O…H-O hydrogen bonding mode and revealed the EE cloud penetration phenomenon to the solvent water molecules. Hydration on C site can increase the EE distribution at the C atom and thus reduce the C…H distance in the C…H-O hydrogen bonds, and inversely, localization of the EE at the C also further increase the number of the coordinating water molecules. The number of water molecules of the C02-anion in the first hydration shell is about4-7. It should be noted that in all our AIMD simulations, no dimer-core (C2O4(?)) and core-switching are observed in these CO2aqueous surroundings.2. Evolution of dielectrons in water solution.We approach series of problems that about dielectron in water solution such as, the electronic evolution features as well as the differences between the corresponding electronic states of singlet and triplet dielectron. The singlet e22"aq initially mainly presents as the diffusion state. The electronic state converts between the localization state and the diffusion state, but mainly as the diffusion state. Until to about5ps, e2--aq survive in a cavity composed of5H2O molecules reoriented by pointing their dangling H atoms toward the trapped singlet dielectron, forming a hydrated dielectron. Such hydrated dielectron exists about lps and then exhibit a novel proton transfer process, generating a hydrated hydride anion (H-). Then the second hangling H atom migrate toward H-resulting in a molecular hydrogen (H2) formation. In the concerted manner,the yielded residue hydroxide anion (OH-) and the other solvent water molecules further reorganize to reach a new equilibrium, forming two separated OH-aq structures. The simulation for the singlet dielectron presents the detailed analysis regarding the evolution dynamics of e22"aq for the understanding of the radiolysis-induced reactions in water solution. But for the triplet dielectron, parallel configuration causes repulsion between them, which prevents the diffusing of each other. The triplet dielectron tends to exist separately. One electron is bounded in a solvated cavity just as the single hydrated electron, and the other electron presents as the diffusion state in different locations. Calculations for the vertical excitation energy of singlet and triplet suggest that dielectron in singlet is stable than in triplet.