Theoretical Study On Local Structure And X-ray Spectra Of Several Fullerene Molecules And Their Chlorinated Derivatives

Fullerene with unique structures and physicochemical properties,as the new kind of carbon nanomaterial,has extensive application prospects in fields of biomedicine,superconducting material and photochemical catalysis,etc.The structure of fullerene is simple,it is composed of pentagonal rings and hexagonal rings connected by carbon atoms.But the different combination modes of pentagon and hexagon cause a large number of isomers for fullerenes,which bring us an obstruction for the future investigation and application of fullerenes.Therefore,structural identification of fullerenes is the most basic and necessary work in fullerenes research.X-ray spectroscopy is an effective tool for exploring the electronic structures and chemical structures of molecules.Its development is one of the most important achievements in the basic science of the last century.The strong sensitivity of X-ray photoelectron spectroscopy（XPS）and Near-edge X-ray absorption fine structure（NEXAFS）spectroscopy to the local structural chemical environment makes them become an important spectroscopy technique for structural recognition.In this article,we systematically researched the XPS and the NEXAFS spectra of three different types of fullerenes(small fullerene C₄₀,large fullerene C₈₄,chlorinated derivatives of fullerenes C₈₆)by means of density functional theory（DFT）and full core-hole potentials.And the feasibility of identifying different types of fullerenes by these two spectral techniques was analyzed.The specific contents and results of the research are as follows:Fullerene C₄₀ is a typical small fullerene.The XPS and the NEXAFS spectra has a strong sensibility to the isomers of C₄₀.The structural characterization of it can be performed by using either of these two spectroscopy techniques.We have also researched the spectra of carbon atoms in different chemical environments and found that the spectral differences between different types of carbon atoms are large.In addition,although the local physical structure of the same type of carbon atoms is the same,due to the large bending and the large difference in local curvature for the small fullerenes,the spectrum produced by the same type of carbon atoms still has some slight difference.Since the XPS of the different isomers of fullerene C₈₄ is very similar,it is difficult to identify their structures by XPS alone.However,the NEXAFS spectra show strong sensitivity to its different isomers.Therefore,the NEXAFS spectra can be used to identify the isomers of big fullerene C₈₄.The spectra produced by different carbon atoms will occur a phenomenon of blue shift with the increasing number of hexagonal rings around them.That is to say,the more the number of hexagonal rings in the local structure in which the carbon atoms are located,the spectra generated by the carbon atoms will move to the high-energy region.And the more the number of pentagonal rings,the spectra will move to low-energy region.Compared to the fullerenes C₈₆,the XPS and NEXAFS spectra of fullerene chlorinated derivatives show obvious blue shift phenomenon,and their spectral changes are more obvious,which reflects the change in the electronic structure of the entire carbon cage after the function of chlorination.The difference between the spectra of the carbon atoms in the same position after chlorination and the corresponding carbon atoms of the parent fullerenes is also larger.The energy of the spectra produced by the carbon atoms which directly connected to the chlorine atoms is approximately 2 eV higher than that produced by other types of carbon atoms.In addition,both of the X-ray spectra we researched shows strong sensitivity to the chlorinated derivatives of these two large fullerenes.However,the XPS of pure large fullerenes C₈₄ and C₈₆ show similarity to some extent,which may be a common phenomenon for large fullerenes.Therefore,it is not advisable to rely on XPS to identify the structures of isomers for large fullerenes in the future.This thesis consists of six chapters:the first chapter is the introduction,It briefly introduces fullerenes,fullerene derivatives and X-ray spectroscopy and describes the research progress of X-ray spectra of fullerenes;The second chapter introduces the basic theoretical methods applied in this thesis and the various approximation methods used in the practical calculation of X-ray spectra;The third chapter introduces the theoretical research and structural characterization of the X-ray spectra for small fullerene C₄₀.It mainly explores the effectiveness of X-ray spectra for structure identification of small fullerene C₄₀ and the influence of the local structure of small fullerenes on X-ray spectra;The fourth chapter introduces the theoretical study and structural characterization of X-ray spectra for large fullerene C₈₄.It mainly investigates the effectiveness of two X-ray spectra to identify the large fullerenes and explores the relationship between the spectra generated by carbon atoms and the number of pentagonal rings and hexagonal rings around them;The fifth chapter mainly researches the effectiveness of X-ray spectra on the identification of fullerene C₈₆ chlorinated derivatives and explores the spectral changes between fullerene chlorides and their parent fullerenes;The sixth chapter summarizes the work of this paper and looks forward to further research.