Investigations Of The Ionization And Dissociation Of N₂O Molecule Collided By Ions With Different Energies And Charged States

Collision experiment is an important tool,in atomic and molecular physics,to obtain the information of atomic and molecular structures and relevant dynamics.The development of reaction microscope and multiple coincidence technique has largely improved the research in atomic and molecular collision physics.The ionization and dissociation of atoms and molecules in collisions with highly charged ions(HCIs)show complex interactions and dynamic mechanisms.Ion collision experiments in high-energy and low-energy regions have been carried out extensively and a variety of collision mechanisms have been suggested.However,the study of ion collisions in the medium-energy region is scarce.In this thesis,medium-energy HCIs impact experiments with molecules are performed using reaction microscope on the 320-kV platform for multidisciplinary research in the Institute of Modern Physics in Lanzhou.The 56 keV/u Ne4+ and Ne8+as well as 5.7 keV/u Xe15+ions are employed to collide with gasous N2O molecule.By measuring fragment ions and the scattered projectile ions with different charges in coincidence,the ion-molecule collision mechanism and the relevant dissociation dynamics are studied in detail using the reconstructed three-dimensional momenta and kinetic energy release(KER)distributions of the fragment ions.In addition,an(e,2e+ion)coincidence spectrometer has been developed in cooperation with Dr.Chen Lei,aiming at the measurement of electron momentum profiles in molecular frame.The thesis consists of six chapters,and the main contents are as follows:In the first chapter,the research background and experimental techniques of ion impact experiments,as well as recent progresses in the studies of the collision mechanisms,dissociation dynamics and molecular geometry reconstruction are introduced.In the second chapter,the experimental apparatus and method of ion-molecule collisions are presented,especially each part of the reaction microscope and the methods for identifying reaction products and determining their momenta and energies.In Chapter 3,the collision experiments of 56 keV/u Ne4+and Ne8+ as well as 5.7 keV/u Xe15+with N2O molecule are reported.The KER distributions of the two-body dissociation channels of N2O2+and N2O3+ions are obtained by multiple coincident measurements and analysis of the fragment ions.With the help of the calculated potential energy curves of the molecular ions,the dissociation paths for each of channels are revealed,and the effect of different energy and different charge of the projectile on ionization and dissociation is also investigated.In Chapter 4,the dissociation mechanism of the multiply charged molecular ion N2Oq+(q=2,3,4)is studied.A novel method is presented to obtain the KER distributions of the delayed dissociation channel and the lifetime spectrum of metastable N2O2+.The dissociation path and the lifetime for the delayed dissociation of metastable N2O2+ are determined.In the study of three-body dissociation of N2O3+and N2O4+,a direct dissociation channel and two sequential dissociation channels of N2O3+,as well as three direct dissociation channels and one sequential dissociation channel of N2O4+ are identified by momentum correlations of the three fragments,and the corresponding physical mechanism is analyzed.In Chapter 5,the momentum correlation angle and KER distributions of the fragment ions are obtained in the Coulomb explosion dissociation of the multiply charged N2Oq+(q=2-6),and the structural parameters of molecular geometry at the dissociation moment are reconstructed through a numerical calculation method.We found that the molecular bond length and bond angle reconstructed according to the dissociation channels,which are well described by the Coulomb explosion model,agreeing well with equilibrium geometry of the neutral N2O.In the sixth chapter,the development of a(e,2e+ion)coincidence spectrometer is introduced,including the overall design and various parts as well as the performance tests of the spectrometer.The ionization and dissociation experiments of CH3I molecule with electron collision were carried out,and the triple coincidence measurement of electron-electron-ion was realized.The electron momentum angular distribution of le orbital along the direction of C-I bond of CH3I was preliminarily obtained,which verified the feasibility of(e,2e+ion)experiment.Finally,the summary of the thesis and the prospect are presented.