The Investigations Of Excitation Dynamic Parameters Of N₂,NF₃ And HCl And The Exploration Of The Double Fluorescences Method

Atom and molecule are the basic elements of the matter,so the research on atomic and molecular properties can extend the knowledgement of the matter structure and advance the understanding to the microworld.The interactions of atoms and molecules with electrons and photons are ubiquitous in the interstellar space,plasma,nuclear fusion,and atomic molecular reaction processes,so the structures and parameters of atoms and molecules are of great significance for the development of many fields,such as astrophysics,atmospheric physics,plasma physics,chemistry and biology,etc.Therefore,developing experimental techniques to improve the accuracy of the dynamic parameters of the excited states of atoms and molecules is not only extremely important to understand the structures of atoms and molecules and the mechanisms of their interactions with the microscopic particles,but also has significant to promote the related disciplines.Fast electron collision method and optical spectroscopy method are important experimental methods to investigate the excitation dynamic parameters of atoms and molecules.Although the fast electron collision method and the photoabsorption method are two completely different experimental methods,there is a close relationship between them and both of them can be used to measure the excitation dynamic parameters of atoms and molecules.Using the fast electron impact method and photoabsorption method,this thesis carried out a series of experimental studies in the excitation dynamics of some atoms and molecules:1.The vibrational structures of both the dipole-allowed(1sσu)-1(1πg)1 and the dipole-forbiddden(1sσg)-1(1πg)1 states of N2 have been observed firstly,and the present experimental results clearly show that the inner-shell 1s core hole of N2 is delocalized over both two N atoms.For a long time chemists and physicists debated the qusetion whether the inner-shell core hole is localized on N atom or delocalized over N2 molecule.In the present work,at an incident electron energy of 1500 eV and an energy resolution of 70 meV,we measurd the electron energy loss spectra of the core shell excitations of N2(1sσg/u→1πg)by the fast electron impact method at 1°-8° scattering degrees.By fitting the measured spectra,the splitting value of the inner shell excitations 1σg/u→1πg was obtained to be 67±7 meV,which supports the hypothesis that the core hole of N2 is delocalized.The momentum transfer dependence behavior of their intensity ratio,i.e.,increasing firstly then decreasing,accords to the theoretical expectations.In addition,the relative Franck-Condon factors of 1Πg(v=0,1,2,3)/1Πg are independent with the squared momentum transfer,which accords to the Franck Condon approximation;2.At an incident electron energy of 1500 eV and an energy resolution of 70 meV,the generalized oscillator strengths and optical oscillator strengths of the valence-shell excitations of NF3 have been measured.The total dissociation cross sections of the dissociative excited states of NF3 have been obtained systematically from the threshold to 2500 eV with the aid of the BE-scaling method.NF3 plays an important role in semiconductor etching,so the dynamic parameters of NF3,especially its total dissociation cross sections,are the most important input parameters for plasma etching modeling and simulation.According to an independent cross-check to the theoretical results,we point out the shortages of the available theortical calculaitions results,and the present BE-scaled dissociation cross sections for the singlet excited states can serve as the benchmark data in plasma models;3.At an incident electron energy of 1500 eV and an energy resolution of 70 meV,the generalized oscillator strengths and optical oscillator strengths of the valence-shell excitations of HCl have been measured and the integral cross sections of the valenceshell excitations of HCl have been obtained systematically with the aid of the BE-scaling method.It is observed that due to the spin-orbit interaction,the wavefunctions of the b3Π1 and C1Πstates are mixed,which results in the generalized oscillator strength ratios of the b3Π1(v’=0)state to the C1Π(v’=0)state being a constant and independent of the squared momentum transfer.The present optical oscillator strengths give an independent cross-check to the previous experimental and theoretical results,and it is found that most of the photoabsorption measurements are limited by the line saturation effect for the strong and narrow transitions;4.In view of the deficiency that the existing experimental methods can not measure the optical oscillator strengths with the high resolution and the high precision simultaneously,the double fluorescences method is proposed to determine the absolute optical oscillator strengths of the vanlence-shell excitations of atoms and molecules and the corresponding spectrometer is designed.According to our experience in electron and photon scattering experiments,the calibration standard is built with the optical oscillator strengths of excitation of 21P of He.The new method is free from the line saturation effect and has the advantages of high resolution of photoabsorption method.By measuring the the fluorescence spectra of Ar atoms at the Hefei National Synchrotron Radiation Laboratory,we prelimiantively tested the performance of the fluorescence spectrometer and provde a scheme for the next improvement.