Theoretical Study Of X-ray Spectroscopy Of Fullerenes And Their Derivatives

Fullerenes and their derivatives have been extensively studied since C60 was discovered in 1985.Significant achievements have been made for the fundamental research and practical applications of fullerene-based materials over the past few decades.Nowadays,more and more fullerene systems have obtained preparations and characterizations experimentally,with broad application prospects in energy,material,medicine and other technical fields.Fullerenes are hollow carbon cages consisting of pentagonal rings and hexagonal rings.Various arrangement forms of pentagons and hexagons result in numerous fullerene isomers,and with increasing carbon atoms the number of fullerene isomers grows rapidly.Thus characterization and identification for fullerene isomers is an important and basic issue in fullerene research.As suggested by the isolated pentagon rule(IPR),adjacent pentagons will bring about high strain and decreased stability of carbon cages,so the separation and synthesis of non-IPR fullerenes will be hampered.However,considering the gigantic proportion of non-IPR isomers in the fullerene family,they have attracted extensive attention and intensive investigations.The research on non-IPR fullerene systems can largely broaden the explorations and applications of fullerene materials.In recent years,a series of non-IPR fullerene structures have been successfully captured by endohedral encapsulation or exohedral derivatization in experiments,undoubtedly largely prompting the fullerene research.X-ray spectroscopies are related with the excitation or de-excitation of core electron.As effective measuring techniques,they have been widely used to explore the electronic and chemical structures of molecules,solids,and surfaces.Particularly,X-ray photoelectron spectroscopy(XPS)corresponds to the ionization process of core electron,which can quantitatively reflect the different chemical environment of specific element.Near-edge X-ray absorption fine structure(NEXAFS)spectroscopy corresponds to the excitation process of core electron from core orbital to virtual orbital,which can provide accurate information of virtual orbitals of the system and further effectively probe the electronic and chemical structures of the system.As suggested by previous research,XPS can show dependence on fullerene isomers of different symmetries,while NEXAFS spectroscopy can show strong isomer dependence for fullerene systems and can be effectively used to identify fullerene isomers.In this thesis,we studied X-ray photoelectron spectroscopies(XPS)and near-edge X-ray absorption fine structure(NEXAFS)spectroscopies of the typical small fullerene C34,three important C56 fullerene isomers and their chlorinated derivatives,and three important C66 fullerene isomers and the related chlorinated derivatives.Following is the brief content of this thesis:C34 is a typical small fullerene.We theoretically calculated the XPS and NEXAFS spectra of six C34 fullerene isomers.The XPS spectra roughly show isomer dependence for C34,and may be mainly used to identify isomers with different symmetries.The NEXAFS spectra show strong isomer dependence for all the six configurations of C34,which can be effectively used to identify different isomers of C34.In addition,we investigated the individual spectra generated by carbon atoms with differene local environment,which clarified the origination of spectral fetures in the total spectra.Further analysis of the individual spectra for carbon atoms in C34 molecules demonstrated that,the spectra generated by carbon atoms in fullerenes are not only determined by the polygons connecting to the exact carbon atom,but also influenced by the tortuosity of the local structure and the outer polygon layers surrounding it.As suggested by early experiments,C56 was the most prevalent small fullerene with intensive mass spectral signals in gas phase,drawing a lot of attention in research.Recently,C2v-#913C56,Cs-#864C56 and D2-#916C56 were successfully captured by exohedral chlorination as #913C56Cl10,#864C56Cl12 and #916C56Cl12,respectively.We theoretically studied the XPS and NEXAFS spectra of the three important C56 fullerne isomers and their chlorinated derivatives.The spectra of the chlorinated species show significant varitions compared with the pristine fullerenes,which distinctly indicated the changes in the electronic structures of carbon cages after chlorination.While the XPS could not show clear dependence on the differene molecular configurations,the NEXAFS spectra show strong isomer dependence for all the three C56 isomers and the chlorinated derivatives,which can be effectively used to identify different molecular configurations.By the investigation of individual spectra generated from carbon atoms with different local environment,we obtained the origination of the important spectral features in the total spectra,and the spectral dependence on local structures of fullerenes was clarified.The spectra generated by carbon atoms bonded with chlorines exhibited a remarkable shift toward higer energies compared with the spectra of the other carbon atoms.C66 is one of the several C2 n fullerenes(2n = 60,66,68,etc)that can be captured by endohedral encapsulation inside the cage,as well as by exohedral derivatization outside the cage.Recently,three important C66 fullerene isomers,C2v-#4059C66,Cs-#4169C66 and C2v-#4348C66,were successfully captured by endohedral encapsulation of two scandium ions or by exohedral derivatization with chlorine atoms.We theoretically studied the XPS and NEXAFS spectra of the three C66 fullerene isomers and the related chlorinated derivatives.Compared with the spectra of C66 molecules,the spectra generated by chlorinated species showed remarkable variations.The XPS showed isomer dependence for the three pristine C66 fullerenes,but not for the chlorinated species.The NEXAFS spectra showed strong isomer dependence for all the studied molecular configurations,and thus could be well employed to identify the three C66 fullerene isomers and the related chlorinated species.By the investigation of the individual spectra for carbon atoms with different local environment,the origination of the important spectral features in total spectra and the spectral dependence on local structures of fullerenes were illuminated.Compared to the spectra of the other carbon atoms,the spectra generated by the carbon atoms connecting to chlorines exhibited a significant blue shift.Theoretical study on the X-ray spectroscopies of the newly synthesized fullerene systems should be basically valuable and stimulative for the further research and applications of them.This thesis consists seven chapters as follows: The first chapter briefly introduces the background of the study of X-ray spectroscopies for fullerene systems.The second chapter includes the basic theories of quantum chemistry which are relevant to this thesis.In the third chapter,we have basically introduced the theoretical methods for the study of X-ray spectroscopies,mainly containing the theories for the calculation of the X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure spectroscopy.The fourth chapter introduces the theoretical study of the X-ray spectroscopies for the C34 fullerene isomers,mainly exploring the validity for the isomer identification using the X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure spectroscopy,as well as the spectral dependence on the local structures of fullerenes.In the fifth chapter,we have introduced the theoretical study of the X-ray spectra for the three newly captured C56 fullerene isoemers and their chlorinated derivatives,in which the exploration of the availability of isomer identification for different molecular configurations using spectra,and the influence on the electronic structures of carbon cages by chlorination,as well as the individual spectra generated by carbon atoms with differenet local environment,has been presented.The sixth chapter introduces the study of the X-ray spectroscopies for the three newly captured C66 fullerene isomers and the related chlorinated species,mainly exploring the validity of the isomer identification for different molecular configurations by spectroscopies,and the variations between the spectra of chlorofullerenes and the spectra of pristine fullerenes,as well as the individual spectra generated from carbon atoms with different local environment.The final chapter includes a whole conclusion for the works in this thesis and presents a prospect for the study of X-ray spectroscopies of fullerenes and their derivatives.