The Study Of Raman Excitation Virtual State Of Molecular Systems And Asymmetry Of Chiral Molecules

In this work, by combining with Raman spectroscopy and Raman optical activity spectroscopy (ROA), we applied the bond polarizability theory to study "the Raman excited virtual state" and related electronic behaviour. This work focuses on molecular bond polarization of Raman excited virtual states by normal Raman spectrum and differential bondpolarizabilities from ROA spectrum and on chemical enhanced mechanism of surface enhanced Raman scaterring (SERS). There are three parts in this work:(1) Studying on the bond polarizability of pyrazine from SERS with time-varying rate effect and its charge transfer process;(2) Studying on the asymmetry of R-Methyloxirane molecules;(3) Studying the asymmetry of β-pinene molecule under532nm excitation.Raman spectroscopy is also known as fingerprint spectra of the molecules, which is widely used in the scientific field of substance identification and molecular identification. Extensive application of Raman spectroscopy is also aroused on the Raman scattering mechanism、+but most of the research works on Raman spectrum have been focused on the measurement and study of peak position, while the large amount of information contained in Raman intensities which is not widely studied. The peak position a molecule (such as infrared, Raman, UV, etc.)is similar, but the peak intensity is different so much, which means that the intensity of Raman spectra contain a large amount of information.Its peak position reflects the molecular structure information. Therefore, it is very important to study Raman spectrum from the point of Raman intensities. The bond polarizability theory is based on the intensity of the Raman spectra and the relation between the molecular polarizability and the the differential value of normal vibration mode. We can obtain the ordinary molecular excitation of the virtual state polarizability, and analyze the electronic behavior of the molecules in the excitation of a virtual state.At the same time, we compared the bond polarizabilit of final Raman excitation state with the ground state.Chirality is of extreme importance in basic physical research, chemical and biological areas.Like the left and right handsto each other, the two chiral molecular are the isomers, they mirror each other but can’t completely coincide with each other. This is the nature of chiral molecules. Excited with the left and right circularly polarized laser, the Raman intensities of chiral molecules have different responses, this is called ROA. Raman optical activity is mainly generated by the coupling of electrice dipole moment and magnetic dipole; there is no difference between the frequencies of ROA spectra and Raman spectra, all the information of the coupling is contained in the intensities of ROA spectra. We combined the theoretical calculation and experimental and study the characteristic so fchiral molecules, further study on chiral structure of chiral molecules and Raman excited virtual state electronic behavior. In addition, we analysed chiral molecular vibration mode and atomic decomposition of contribution through the PyVib2software. We calculated the sign of ROA by classical mechanics and compared with experiments.