Dynamic Parameters Of He,H₂and Na Studied By High-resolution Non-resonant X-ray Scattering And Fast Electron Scattering

Due to the demands of atomic and molecular physics as well as the devel-opment of aerospace industry, laser science, controlled fusion and environmental protection, the investigations of dynamic parameters of atoms and molecules has been one of the most important fronts of atomic and molecular physics. At present, there are two main experimental techniques to study the dynamic parameters of atoms and molecules, which are high-resolution non-resonant X-ray scattering technique and fast-electron scattering technique. The three-dimensional physical information of atoms and molecules, including the excitation energy, momentum transfer and transition intensity, can be determined by either of these two tech-niques, and the information of the wavefunctions of the ground state and excited states of atoms and molecules can also be obtained from the dynamic parameters.High-resolution non-resonant X-ray scattering technique is a new technique in the field of atomic and molecular physics. Using BL12XU beamline in the third-generation synchrotron radiation of SPring-8, for the first time this technique was successfully used to study the dynamic parameters of atoms and molecules by our group in2009, which shows great advantages. Fast-electron scattering tech-nique is the earliest technique to study the dynamic parameters of atoms and molecules, which has being used for several decades and a lot of experimental dy-namic parameters of atoms and molecules have been determined by this technique. Although there is apparent difference between the high-resolution non-resonant X-ray scattering technique and the fast-electron scattering technique, they have close relationship, and jointly promote the research of dynamic parameters of the atoms and molecules.In this thesis, the following works are reported:(1)Using the high-resolution non-resonant X-ray scattering technique, the elastic squared form factors of molecular hydrogen were measured for the first time, and its momentum transfer dependence behavior was studied. For molecules, due to the interference between the scattering of separate nuclei and the scattering of the electrons in the target, the elastic squared form factors cannot be deter-mined by the high-energy electron impact method. So the high-resolution X-ray scattering technique has the unique advantages in the study of the electronic structure of atoms and molecules in the ground state.(2) Using the high-resolution non-resonant X-ray scattering technique, the elastic squared form factor of atomic helium were measured, and its momentum transfer dependence behavior was studied. Unlike molecules, the elastic squared form factors of atomic helium can be obtained from the elastic differential cross section measured by high-energy electron scattering under the first-order Born approximation. By comparing the results of high-energy electron scattering with the X-ray scattering ones, it is found that in the small momentum transfer region the differential cross section of electron scattering is sensitive to the contribu-tion beyond the first-order Born approximation, because the scattering amplitude between the incident electron and the nuclei almost offsets the first Born scat-tering amplitude between the incident electrons and the electrons in the target. In the large momentum transfer region, the elastic differential cross sections of electron scattering are almost due to the contribution from the nuclei scattering, so it is very difficult to test the electronic structure. However the differential cross sections of the X-ray elastic scattering is only due to the contribution from the target’s electrons, so X-ray scattering is very suitable to test the electronic structure of atoms in the large momentum transfer region. In one word, the elastic differential cross section measured by the high-energy electron scattering can strictly test the validity of the first-order Born approximation in the small momentum transfer, and the elastic squared form factors measured by the high-resolution non-resonant X-ray scattering can strictly test the wavefunctions in the inner region.(3) By analogizing to the Dipole(e,e) method, our group proposed a new method to determine the absolute optical oscillator strengths of atoms and molecules using the high-resolution non-resonant X-ray scattering technique at a very small momentum transfer, i.e., q2≤0.01a.u., for the first time, and it is called as Dipole(γ,γ) method. Using the Dipole(γ,γ) method, the absolute optical oscilla-tor strengths of Lyman and Werner bands of molecular hydrogen are determined. The optical oscillator strengths of Lyman and Werner bands of molecular hydrogen obtained by Dipole(γ,γ) method are agreement with the previous experimental and calculated results, which indicates the validity of the Dipole(γ,γ) method.(4) The author updated the high-resolution fast-electron energy loss spec-trometer in2012-2013, so there is a great improvement of the vacuum, stability of the spectrometer. With the high-resolution fast-electron energy loss spectrometer and the newly designed metal-vapor oven, the generalized oscillator strengths of valence-shell excited states of atomic sodium were studied preliminarily with a high incident electron energy of1500eV and a high energy resolution of70meV. Due to the pressure effect, the generalized oscillator strengths of32P and42P deviates from the results calculated by the first-order Born approximation. The generalized oscillator strengths of42S,52S,42D+42F+52P and52D+52F+52G+62S are in good agreement with the results calculated by the first-order Born approx-imation, which indicates the first-order Born approximation at incident electron energy E0=1500eV is satisfied.