The Study Of Ion-atom Collisions In The Low Energy Region

Heavy particle collisions refer to the reactions between ions and atoms/molecules,including excitation, charge transfer, ionization, and radiative decay processes etc.There are extensive heavy particle collisions processes present in astrophysics andlaboratory plasma etc environments, where the heavy particle collisions ratecoefficients are much larger than the ones of electron collisions due to the very lowelectron density and temperature, which plays a dominant role in the ionizationbalance and the energy transport of plasma and the cross sections of differentscattering processes become the fundamental atomic parameters required in theplasma simulations. In the present paper, the collisions of Li-(1s22s2)-H(1s),H-(1s2)-Li(1s22s) and Be+(1s22s2S)+He(1s2s) are studied, which are of great interestin some related area studies. The Li--H/H--Li collisions play an important role in theearly universe evolution and the liquid lithium divertor will be applied in the nextgeneration magnetic confined fusion reactors equipments (for example TOKAMAKand ITER); and there are rich Be ions and excited He atoms present in the divertorand edge plasma areas of TOKAMAK.In the present studies, the ab initio multireference single-and double-excitationconfiguration interaction (MRD-CI) method is applied to compute the molecularelectronic structures of LiH-and the collisions complex of Be+(1s22s)-He(1s2s),including the potential surfaces, the dipole transition matrix element, the radial androtational coupling matrix elements. For LiH-system, the lowest six2+and two2 states have been considered in the MRD-CI and scattering calculations, which arecorresponding to Li(1s22s)+H-(1s2), Li-(1s22s2)+H(1s), Li-(2s2p3P0)+H(1s), Li-(2s3s3S)+H(1s), Li-(2s2p1P0)+H(1s), Li-(2s3s1S)+H(1s), Li-(2s2p3P0)+H(1s) and Li-(2s2p1P0)+H(1s) in the asymptotic regions. For Be+(1s22s)-He(1s2s) collisions complex, thelowest five2+and two2Be(1s22s21S)+He+, Be(1s22s2p3P0)+He+, Be+(1s22s2S)+He(1s2s3S), Be(1s22s2p1P0)+He+, Be+(1s22s2S)+He(1s2s1S), Be(1s22s2p3P)+He+and Be(1s22s2p1P)+He+in the asymptotic regions. In the potential surface calculations, the computationalerrors in the asymptotic energies are less than0.1eV in comparison with the availableexperimental and theoretical data, which meets with the computational accuracyrequired in the scattering dynamic studies.The quantum-mechanical molecular-orbital close-coupling method has beenapplied to investigate the charge transfer and excitation processes in the collisions ofLi--H and H--Li. The hydrogen and lithium anions will be produced in the excitationand charge transfer processes and the electron dissociation process will happen if theunstable anion resonance states are formed. For Be+-He(1s2s) collisions, the fullyquantum, optical-potential, and semiclassical methods have been applied toinvestigate the radiative charge-transfer, radiative-decay, and radiative-associationprocesses in the energy range of10-10eV-1eV. From the views of the fundamentalstudy, different processes in ion-atom collisions have been investigated, includingexcitation, charge transfer, and the following radiative association and electrondetachment etc, and the corresponding reaction mechanisms have been discussed, forexample the transition driven by radial coupling, rotational coupling, dipole transitionetc. From the views of application, the present work can provide important atomicdata required in the spectrum simulation in astrophysics and the plasma simulation inmagnetic fusion science, including different kinds of scattering cross sections andreaction rate coefficients.