Analysis And Assignment Of The Spectra Of A Salt/Solution System

With the important application in science and practice, the microstructure andproperties of salt solution have attracted great interests of chemists. It has become a hottopic to investigate micro-structure and nature of water and non-water solution from themolecular level, which help to understand the phenomenon and nature of the macro. Itsapplication penetrates into a variety of cutting-edge disciplines such as chemistry, chemicalengineering, life science, materials science and so on. Thus it has the important theorysignificance and practical prospect. In this paper, on the basis of previous work, ion-ion andion-solvent interaction have been studied in different salt solution from multiple aspects byinfrared spectroscopy, molecular fluorescence spectroscopy and density functional theory（DFT）. The main contents of the present work are as follows:1. Infrared spectroscopy is applied to study different concentration and temperatureCaCl₂/methanol solution. It is found that the solvation number decreases with increasingtemperature. Through the theory calculation, it could be concluded that the main complexesforms are [CaCl（CH₃OH）_n]⁺（n=3-5） and [Cl（CH₃OH）_n]^-（n=2-4）. DFT is also used topresume the stable forms of CaCl₂in water and ethanol, and its change tendency astemperature rising.2. DMF, different concentration LiCl/DMF and LiNO₃/DMF solution havebeen investigated by infrared spectroscopy and DFT. It is concluded that theproportion of the solvated DMF molecular decreases with temperature increase,while the proportion of ion pair form increases. Comparing the experiment andcalculation spectra, it is found that the main complexes forms are ion pair forms（LiCl（DMF）_nand LiNO₃（DMF）_n）, a few cation （[Li（DMF）_n]+） and anion（[Cl（DMF）_n]^-and [NO₃（DMF）_n]^-） forms.3. Fluorescence spectroscopy of CaCl₂, LiCl and Ca（NO₃）₂in methanol have beeninvestigated. Through the structure optimized and excitation energy, it is found that theclusters of [CaCl（CH₃OH）_n]⁺and LiCl（CH₃OH）_nhave fluorescence property, theoscillation intensity of NO3-and methanol clusters is almost zero. This illustrates thefluorescence reinforcing phenomenon of CaCl₂and LiCl in methanol, and the fluorescencequenching phenomenon of Ca（NO₃）₂in methanol.4. The fluorescence spectroscopy is used to research methanol-water and inorganicsalt in methanol-water solution. It is found that methanol-water solution has fluorescenceproperty, different salts and volume proportions of methanol and water have differenteffects on fluorescence spectroscopy. Excitation wavenumber of various clusters has beencalculated by TD-DFT. And it is concluded that ion kinds and solvation number consistedclusters have effect on the fluorescence spectroscopy.