The Development Of(e,e+ion)Spectrometer And The Studies Of Electron-Impact Molecular Dissociative Ionization

The excitation,ionization and dissociation of atoms and molecules in collision with electrons,ions or photons are the basic contents of atomic and molecular physics.The information on the scattering,structure and dynamics of atoms and molecules can be obtained by measuring the energy and momentum of the products from the collision reaction.With the development of experimental techniques,especially the emergence of momentum imaging,reaction microscope and velocity imaging techniques,the excitation,ionization and dissociation of molecular systems have drawn an extensive attention.Photo-excitation experiments can select specific molecular excited states or ionic states by adjusting photon energy,but subject to the limits of optical selection rules.Electron collision is free of such limits considering the momentum transfer,which is a complementation of the optical method.However,electron spectroscopy has its limits in the energy resolution and detection efficiency.The main work of this thesis is the development of electron-impact methods to research the state-selective molecular excitation and dissociative ionization.On the basis of ion imaging spectrometer,an energy analyzer is introduced to collect the scattered electrons after collision,consequently a(e,e+ion)spectrometer is developed.Through the measurement of the scattered electrons and dissociated ions,the state-selective studies for electron-impact molecular dissociative ionization are carried out to reveal the effects of different electron energy losses and momentum transfers on molecular excitation and dissociative ionization.Moreover,the fragmentation dynamics study of OCS molecule in collision with electron and the absolute electron-impact ionization cross sections measurement of N2 are carried out by ion momentum spectrometer.This thesis is consisted of five chapters.The details of each chapter are described as follows:The first chapter introduces the experimental techniques for studying molecular dissociative ionization in atomic and molecular physics,the recent advances in molecular dissociative ionization experiments,and the current status of the state-selective electron-impact molecular dissociative ionization studies.The second chapter presents the development of(e,e + ion)spectrometer.Employing the electron-impact N2 single ionization and dissociation experiment,the(e,e+ion)spectrometer is validated through the scattered electron-ion kinetic energy correlation and the angular distribution of the N+relative to the momentum transfer.The third chapter introduces the experimental work of the dissociative ionization of CO using the(e,e+ion)spectrometer.The KER of C++O+under different energy losses and the yield of C++O+under different KER experimentally confirmed the three mechanisms for producing C++O+near the CO double ionization threshold.Besides the angular distributions of C+ relative to electron momentum transfer produced by the three mechanisms are distinct.The fourth chapter introduces the study of fragmentation dynamics of OCS in collision with electron.The dissociation mechanisms of OCS molecular ions are analyzed by ion momentum correlation.For the first time,the sequential fragmentation pathways of OCS molecular ions are found by electron collision.The KER distributions of each dissociation channels are analyzed.The fifth chapter presents the absolute ionization cross section data of N2 at the electron-impact energy from 250 eV to 8000 eV measured by a scaled method of the relative flow in mixed gases.For the first time,the absolute PICS data of N2 above 1000 eV is offered.Summarization and prospects are given at the end of the thesis.