Spectroscopy And Theoretical Calculation Research On The Microstructures Of Zn²⁺ Solution

Research on microscopic structure of ions in the solution is an important part of the modern study of physics, chemistry, biology. By studying solvation phenomenon can help people know the form of the structures in salt solution, thus the research can provide strong basis for many chemical reaction mechanism and ion transport in biological system. According to the chemical bonding theory, chemical reaction mechanism, the interaction force between molecules and various kinds of spectral knowledge have become a popular method for studying the microscopic particles in quantum chemistry. Quantum chemistry can be better applied to the explanation of experimental results, research on molecular interactions, the predicting of molecular stability and regularity of chemical activity, etc with the application of computer technology and the development of ab initio calculations. This article is based on the predecessors'work and density functional theory, Combining the calculation by GaussianO9 software with the experiments of fluorescence spectrum, Raman spectrum experiment of salt solution to study the microscopic structure of clusters. The main research contents are as follows:The cluster structures of [Zn-(CH3CH2OH) n]2+have been investigated by spectroscopic experiment and theoretical calculation. According to the the fluorescence spectroscopy experiments, we found that the fluorescence intensity of ethanol changed and a new peak generated after the metal ions (Zn2+) added into ethanol solution. The cluster structures of Zn2+in water solution were investigated by using different methods. Through the comparing of the results, the more accurate and fast B3LYP method of DFT was found and applied to optimize the possible structures of [Zn-(CH3CH2OH)n]2+. The results suggested that the first solvation shell of the system is up to six ethanol molecules, and thermodynamic parameters also shows the six kinds of molecular clusters which are likely in the solution. Moreover compared the theoretical fluorescence spectroscopy with experimental fluorescence spectroscopy, new clusters [Zn-(CH3CH2OH) n]2+have generated, which proved the feasibility of the calculation methods.We studied Raman spectra from 50 cm-1-4000cm-1 excited at 633nm for pure water and different concentrations of solution. According to the Raman spectra experiment we found new peaks at 230cm-1-340 cm-1 and 370cm-1-540cm-1 compared with pure water, which caused by the vibration of O-Zn-Cl of new clusters, indicating that new molecular clusters formed in solution after zinc salt added into water. Theoretical calculations take coordination competition between H2O and Cl" into account, firstly B3LYP was applied to structural optimization and frequency calculations for the ion pairs of [ZnCl] 2-n (n= 1-4). Secondly, the clusters of Zn2+and the possible ion pairs in water were investigated by B3LYP.The vibration modes of possible clusters and the Raman intensity were found though Raman calculations.According to the bond length,charge, energies and comparing the theoretical and experimental spectrum,we found the clusters of ZnCl2 in water were mainly composed by [Zn-(H2O) 6]2+, [ZnCl-(H2O)]+, [ZnCl2-(H2O)].Different concentrations of ZnCl2/H2O solution were measured by Raman spectra. Through the comparison of different concentration of Raman spectra,we found that the characteristic peak at 3054 cm -1-3728-cm'1 became weak with the increase of salt concentration, however when the concentration came to 0.3mol·L-1, the characteristic peak became strong with the increase of salt concentration. And the influence of new peak at 230 cm"1-340cm-1 is small at low concentration however the intensity of new peak became strong at high concentration. The results showed that anionic (Cl-) has less effect on Zn2+in low concentration, when in relatively high concentrations the impact of (Cl-) can not be ignored. We also measured the Raman spectra at different temperatures, it was found that temperature have a greater influence on the conformation of clusters in low temperature range, have little effect in high temperature range. The possible clusters in salt solution were calculated at different temperatures, the temperature influence on clusters were proved by the results of energy and thermodynamic parameters.