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Register a new userState selective differential cross sections for single and double electron capture in $Hesp{1,2+}-He$ and $p-He$ collisons
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Added by
Markus Sch\\\"offler S.
Publication date
2007
fields
Physics
and research's language is
English
Authors
M. S. Schoffler
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Using the COLTRIMStechnique, scattering angle differential cross sections for single and double electron capture in collisions of protons and $Hesp{1,2+}$ projectiles with helium atoms for incident energies of $60-630 keV/u$ are measured. We also report new theoretical results obtained by means of four-body one-channel distorted wave models (CDW-BFS, CDW-BIS and BDW), and find mixed agreement with the measured data.
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The absolute electron capture cross sections for single and double charge exchanges between the highly charged ions O6+ and CO2, CH4, H2, N2, the dominant collision processes in the solar wind, have been measured in the energy from 7 keV*q (2.63 keV/u) to 52 keV*q (19.5 keV/u). These measurements were carried out in the new experimental instrument set up at Fudan University, and the error of cross sections for single and double charge exchanges at the 1{sigma} confidence level are about 11% and 16%, respectively. Limited agreement is achieved with single electron capture results calculated by the classical over-barrier model. These cross sections data are useful for simulation ion-neutral processes in astrophysical environments and to improve the present theoretical model of fundamental atomic processes.
The cross-sections and analyzing powers for $(p,n)$ reactions on ${}^{3}{rm He}$ and ${}^{4}{rm He}$ have been measured at a bombarding energy of $T_p$ = 346 MeV and reaction angles of $theta_{rm lab}$ = $9.4^{circ}$--$27^{circ}$. The energy transfer spectra for ${}^{3}{rm He}(p,n)$ at large $theta_{rm lab}$ ($ge$ $16^{circ}$) are dominated by quasielastic contributions, and can be reasonably reproduced by plane-wave impulse approximation (PWIA) calculations for quasielastic scattering. By contrast, the known $L$ = 1 resonances in ${}^{4}{rm Li}$ are clearly observed near the threshold in the ${}^{4}{rm He}(p,n)$ spectra. Because these contributions are remarkable at small angles, the energy spectra are significantly different from those expected for quasielastic scattering. The data are compared with the PWIA calculations, and it is found that the quasielastic contributions are dominant at large $theta_{rm lab}$ ($ge$ $22^{circ}$). The nuclear correlation effects on the quasielastic peak for ${}^{4}{rm He}(p,n)$ are also discussed.
A general formalism is used to express the long-range potential energies in inverse powers of the separation distance between two like atomic or molecular systems with $P$ symmetries. The long-range molecular interaction coefficients are calculated for the molecular symmetries $Delta$, $Pi$, and $Sigma$, arising from the following interactions: He($2 ^1P$)--He($2 ^1P$), He($2 ^1P$)--He($2 ^3P$), and He($2 ^3P$)--He($2 ^3P$). The electric quadrupole-quadrupole term, $C_{5}$, the van der Waals (dispersion) term $C_{6}$, and higher-order terms, $C_{8}$, and $C_{10}$, are calculated textit{ab initio} using accurate variational wave functions in Hylleraas coordinates with finite nuclear mass effects. A comparison is made with previously published results where available.
We have used the convergent close-coupling method and a unitarized first-order many-body theory to calculate integral cross sections for elastic scattering and momentum transfer, for excitation of the 5d^2 ^1S, 6s6p^1P_1, 6s7p^1P_1, 6s8p^1P_1, 6s5d^1D_2, 5d^2^1D_2, 6s6d^1D_2, 6p5d^1F_3, 6s4f^1F_3, 6p5d^1D_2, 6s6p^3P_{0,1,2}, 6s5d^3D_{1,2,3}, and 6p5d^3D_2 states, for ionization and for total scattering by electron impact on the ground state of barium at incident electron energies from 1 to 1000 eV. These results and all available experimental data have been combined to produce a recommended set of integral cross sections.
We report on kinematically complete measurements and ab initio non-perturbative calculations of double ionization of He and H2 by a single 800 eV circularly polarized photon. We confirm the quasifree mechanism of photoionization for H2 and show how it originates from the two-electron cusp in the ground state of a two-electron target. Our approach establishes a new method for mapping electrons relative to each other and provides valuable insight into photoionization beyond the electric-dipole approximation.
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