Molecular Spin - Orbit Coupling And Jahn-teller Effect Of High Energy Resolution Electron Momentum Spectroscopy Study

The investigations on relativistic effects for CF₃I and Jahn-Teller effect for cyclopropane have been carried out by the high-energy-resolution electron momentum spectrometer.The splitting of the ionization bands for the highest occupied molecular orbitals(HOMO)of this two molecules induced respectively by the two effects have been observed,and the experimental momentum profiles(XMPs)for the splitting bands and the corresponding branching ratio have also been obtained.The obvious differences between the XMPs of the splitting components exhibit relativistic effects and Jahn-Teller effect on the electronic wavefunctions,and have been explained rationally on the basis of the quantum chemistry calculations.In addition,the studies of the electronic structures,the bonding characters and the fluorine-substituted effects for CH₂BrCl and CF₂BrCl by the low-energy-resolution electron momentum spectrometer are presented in this dissertation.Seven chapters are included as followings:The orbital-image techniques are outlined together with the applications and the recent advances of the electron momentum spectroscopy(EMS)studies in Chapter 1.The basic principles including the theoretical background and the computational methods are described in Chapter 2.Chapter 3 introduces the experimental methods.Chapter 4 includes the introductions of spin-orbit coupling effects and Jahn-Teller effect.The EMS studies on relativistic effects for the 5e orbital of CF3I are presented in detail in Chapter 5 together with the 5α₁ orbital.The binding energy spectrum and the XMPs for the two spin-orbit splitting components 5e_3/2and 5e_1/2have been measured by high-resolution-energy electron momentum spectrometer.The XMPs of the two components 5e_3/2and 5e_1/2exhibit obvious different intensities and can not been explained by non-relativistic wavefunctions.Considering the iodine lone-pair character of 5e,a qualitative explanation exhibiting relativistic effects on molecular orbital wavefunctions are presented according to the relativistic studies on radial charge densities for atoms.Comparing with the theoretical momentum profiles(TMPs) calculated by all-electron basis sets,the TMPs calculated by relativistic effective core potential(ECP)basis sets better describe the XMPs of 5e(5e_3/2+5e_1/2)and 5α₁, showing relativistic effects from inner electrons on the electron momentum distributions of valence electrons.Moreover,the comparisons of the XMPs of correlated orbitals for CH3I and CF₃I indicate the fluorine-substituted effects on electronic structures and the bond characters.Chapter 6 focuses on the Jahn-Teller effect on the XMPs of the two splitting components(namely 1-JT and 2-JT)for cyclopropane.The intensities of 1-JT are generally 1.85 times greater than those of 2-JT,while in the low momentum region the intensities of 2-JT become larger than 1-JT,which are different from the observations of the previous EMS studies.Combined with high-level quantum calculations,our observations are understood at the static and dynamic aspects, especially according to an extreme picture presented by E.Haselbach.In addition,the assignments of 3α′₁ and 1α″₂ are clarified by comparison of XMPs with TMPs.Chapter 7 introduces the EMS studies on the electronic structures of CH₂BrCl and CF₂BrCl carried out by poor-energy-resolution electron momentum spectrometer, including the discussion of bonding characters,the achievement of the pole strength for the inner valence orbitals of CH₂BrCl and the determination of some amphibolous orbitals of CF₂BrCl.