The Study Of The Dynamic Parameters Of H₂,D₂ And N₂ By Inelastic X-ray Scattering

Excitation and deexcitation of atoms and molecules extensively exist in nuclear fu-sion,plasma,interstellar space,planetary atmosphere and chemical reaction processes.It is of great significance to study the excitation properties of atoms and molecules which benefits the development of plasma physics,astrophysics,physical chemistry and other disciplines.The excited properties of atoms and molecules include their energy level structures and the dynamic characteristics,which are often described by the dynamic parameters reflecting the information of the wavefunctions of initial and final states.In the field of atomic and molecular physics,the dynamic parameters are mainly described by the cross sections,oscillator strengths and squared form factors.With the develop-ment of the modern spectroscopy technique,the measurement of the energy levels can reach a very high precision(<10-16).However,the measured dynamic parameters are still in a limited precision.Experimentally,the dynamic parameters of atoms and molecules are mainly studied by the optical method,electron scattering method,ion col-lision method and X-ray scattering method.X-ray scattering is a novel method,which was first used in the study of atomic and molecular dynamics parameters in 2009 by our groups.Later,our group developed the dipole(?,?)method,which is used to obtain the optical oscillator strengths of atoms and molecules.Besides,our group constructed an inelastic X-ray scattering spectrometer at BL 15U beamline in Shanghai synchrotron radiation source which focuses on the study of the dynamic parameters of inner-shell excitations of atoms and molecules.In this dissertation,we determine the optical oscillator strengths of Lyman band and Werner bands of H2 and D2 based on the dipole(?,?)method,in which the energy resolution is improved from 70 meV to 25 meV.In addition,the IXS spectrometer in Shanghai synchrotron radiation source is tested and debugged.And the generalized os-cillator strengths(GOSs)of the inner shell excitation of N2 are measured to calibrate the spectrometer.The contents of this thesis includes:(1)The energy resolution and signal to noise ratio of dipole(?,?)method have been improved greatly by using a position sensitive detector and a better collimation and shielding system.The energy resolution of the spectrometer is increased from 70 meV to 25 meV and the background count is suppressed to almost one counts per 100 seconds.Under such a condition,the optical oscillator strengths of Lyman band and Werner band of H2 have been measured.Through the comparison of experiments and theory,we find that the present results of v'>6 of Lyman band are obviously differ-ent from the results of the previous photoabsorption method,the fast electron collision method having a slightly poor energy resolution,and the theoretical calculations within the scheme of Born-Oppenheimer approximation.However,our results are in good agreement with the theoretical calculations when the electron-vibration coupling effect is considered.As for Werner band,the present results fit well with all other experimen-tal and theoretical results.It suggests that the electron-vibration coupling effect has obvious influence on the optical oscillator strengths of Lyman band of H2,while it is weak for the Werner band;(2)The optical oscillator strengths of molecular D2 have been measured by experi-ment for the first time.Compared the present results with the theoretical results,neither the Lyman band nor the Werner band of D2 shows strong electron-vibration coupling ef-fect.In addition,we also analyse the electronic transition moments of D2.Through the comparison with the experimental and theoretical results of H2,we observe the slight difference due to the isotope effect;(3)The previous applications of inelastic X-ray scattering method in the study of atomic and molecular dynamics parameters are limited in the valence-shell excitations of atoms and molecules.We constructed an inelastic X-ray scattering spectrometer with an energy resolution of 1.4 eV at BL 15U beamline in Shanghai synchrotron radiation source.The spectrometer dedicates to study the dynamic parameters of inner-shell ex-citations of atoms and molecules.After the optimization of the spectrometer,the gen-eralized oscillator strengths of the inner shell excitations of N2 have been determined for the first time with the inelastic X-ray scattering technique.The present results show that the spectrometer has reach its design targets which gives a solid foundation to the dynamic parameter studies of the inner-shell excitations of atoms and molecules.