The Relativistic Effect In Electron Momentum Distributions Of Atoms And Molecules

Electron momentum spectroscopy(EMS)can simultaneously obtain the information of energy and momentum distribution of orbital electrons and has become an important technique for the investigation of electronic structures of atoms and molecules.EMS also has unique advantages in terms of studying the relativistic effects.It can exhibit the relativistic effects in two domains,the binding energy and the orbital wave function.In this dissertation,the relativistic effects of atoms and molecules are studied using a full-angle electron momentum spectrometer in our lab and quantum chemical calculations.Firstly,the relativistic effects of the highest occupied orbitals of 2-iodopropane(2-C3H7I)molecule were studied by comparing the ratio of the electron momentum distributions for the two spin-orbit splitting components 5a" and 8a' with the quantum chemical calculations.Secondly,the spin-orbit two-component relativistic method is used to calculate the electron momentum distributions of the two spin-orbit splitting components 4d5/2 and 4d3/2 of 4d orbital of Xe atom as well as the corresponding ratios,and the results are compared with the experiments available.Finally,the relativistic effect on the electron momentum distributions of the spin-orbit splitting components 4d5/2 and 4d3/2 of methyl iodide(CH3I)was studied.The electron momentum distributions and interference effect for the outer valence orbitals of the SF6 molecule were also investigated using the full-angle electron momentum spectrometer.The thesis is comprised of seven chapters:The first chapter briefly reviews the research of relativistic effects,introduces the EMS experimental methods and the motivations of thesis work.The second chapter introduces the full-angle(e,2e)electron momentum spectrometer,including the construction of the spectrometer,data acquisition system,data processing method,and introduces the theoretical framework of EMS,and several commonly used methods for electronic structure calculations.The third chapter introduces the EMS study of the 2-C3H7I molecule.For the first time,the electron momentum distributions and the corresponding ratio of the spin-orbital splitting components 5a" and 8a' of the highest occupied orbital are obtained.Theoretically,the relativistic effect on the 2-C3H7I molecule was analyzed using Amsterdam Density Functional(ADF)quantum calculation software,by carrying out a spin-orbit two-component and pseudopotential relativistic calculations.Studies showed that the relativistic effect has a significant effect on the orbital wave functions of the spin-orbit splitting components 5a" and 8a' of the highest occupied orbital and the orbital wave function of C-I bond orbital 7a'.Studies also show that molecular vibrations can greatly affect electron momentum distributions for 6a'+4a"and 3a"+2a" orbitals.In the fourth chapter,the two-component relativistic method is used to calculate the electron momentum distributions of the spin-orbit coupling splitting components 4d5/2 and 4d3/2 of the 4d orbital of Xe atom and the corresponding ratio of the two components.The results are in good agreement with the experimental data measured by Ren et al.At the same time,considering the influence of the distorted wave effect at the low momentum region,the electron momentum distribution of the Xe 4d orbital is calculated by the distorted wave Born approximation(DWBA)method.The fifth chapter introduces the results of CH3I molecule.The electron momentum distributions of the spin-orbit splitting components of the core-shell orbital 4d5/2 and 4d3/2 and corresponding ratio of the two components have been obtained.The experimental results were analyzed by the theoretical calculations carrying out using the relativistic density functional method.Studies have shown that the relativistic effect results in the difference in electron momentum distributions for the two spin-orbit splitting components.Due to the difficulty in calculating the distorted wave effect for molecule,we carried out DWBA calculations for 4d orbital of I atom.The results show that the turn-up in the low momentum region in the electron momentum distribution of 4d orbital of CH3I molecule can be ascribed to the distorted wave effect.The sixth chapter introduces the EMS study of the outer valence shell of the SF6 molecule.The binding energy spectrum and electron momentum distributions of the outer valence orbitals are obtained.With the help of theoretical calculations based on the density functional method,the experimental results were analyzed and explained.For molecular orbitals(lt1g,lt2u+5t1u,3eg),the multi-center interference effects were observed,and the experimental and theoretical ratios and interference factors are in good agreement with each other.The seventh chapter summarizes the works of this thesis and prospects the future experimental and theoretical work.