The Raman Spectra and the Cluster Structures of Ethylene Carbonate Solutions Studied by the Gaussian 09 Molecular Simulations
| Autor: | Huang, Jyun-Ying, 黃俊穎 |
|---|---|
| Rok vydání: | 2017 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 105 Ethylene carbonate (EC) has Fermi resonance between fundamental ν2 and overtone 2ν7 indicated by their Raman band’s coupling separation (Δ). In normal situation, we know that the line intensity of fundamental is much higher than overtone. However, the energy of both lines would be redistributed by the Fermi resonance, and result in a significant decrease of the intensity ratio R(=ν2/2ν7). In our previous study, we have found that Δ and R match up to the expectation of Herzberg’s theory by exploring the Fermi resonance Raman spectra of EC aqueous and methanol solutions. In this study, we examine the Raman spectra of the Ethylene Carbonate (EC)’s Fermi resonance by utilizing the Gaussian 09 molecular theoretical simulation, and explore their correlations with the local cluster structures. Many facts emerge that Gaussian 09 doesn’t consider Fermi resonance into the simulated calculation, and this turns out to be our entry point in the study. That is to say, previously obtained Δ0 (~15.7 cm-1) and R0 (~5) can be use as references in the Gaussian 09’s simulation work. According to the simulated results of Δ0, we found that there are three water molecular adsorb on the chain cluster structure formed by four EC molecular in the EC aqueous solution (abbreviated tetramer+3), and its scaling factors also match the numerical range offered by National Institute of Standard and Technology. Because the hydrogen bond of methanol solution is probably weaker than that in aqueous solution, there are three simpler cluster structures in the EC methanol solution: two or three water molecules adsorbed on one EC molecule (abbreviated monomer+2 and monomer+3), or three water molecules adsorbed on EC dimer (abbreviated dimer+3). Additionally, the Gaussian 09 software doesn’t show any data of overtones, and neither offering the option of calculation of polarizability’s second derivatives to normal mode. But, we propose an approximate and simply estimated method for calculating the intensity ratio (R0) of the two modes without Fermi resonance. We found that the R0 of the cluster structures mentioned above are much smaller than experimental value (~5). On the contrary, the EC monomer’s R0 (~7.2) is much closer to the observed value. It probably indicates that our approximate method isn’t suitable for complicated cluster structure, and may also imply that there is low correlation between the Fermi resonance Raman spectra’s intensity ratio and the cluster structure. It perhaps partially explains our previous conclusion, that is “Δ0 and R0 are in low correlation with solvents.” |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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