Positron impact ionisation of He ion

Triple differential cross-sections (TDCS) of a hydrogenic (He⁺) ion has been studied by positron impact using coplaner geometry for both symmetric and asymmetric kinematics in the intermediate and medium high incident energy region. TDCS has also been studied of He⁺ ion by electron impact for symmetric kinematics taking account of the electron exchange effect. The final state wavefunction is chosen as the correlated 3-body Coulomb wavefunction satisfying the exact asymptotic boundary condition. The long range Coulomb interaction in the initial channel between the ionic target and the projectile has also been taken into account properly. For positron impact, the collision is found to be almost recoilless at lower incident energies, in contrast to the strong recoil peak noted in the case of electron impact ionisation. For electron impact, the exchange effect is found to be significantly high for equal energy sharing in the final channel. Received 10 July 1999 and Received in final form 7 December 1999     

Ionization of metastable He(1s2s) atoms by alkalated surfaces

We calculate the ionization probability for singlet and triplet metastable He(1s2s) atoms scattered from potassium covered surfaces, on the basis of the resonant tunnelling process. We do not assume the trajectory approximation, but we do assume classical motion on the potential energy curves, with crossing between neutral and ionic curves at a given point calculated from electronic tunnelling probabilities. Energy spectra of the He⁺ ions are also calculated. The results are found to be somewhat sensitive to tunnelling probability as a function of distance from the surface. Results are compared with experimental ionization probabilities measured by Roussel. The agreement is found to be fair if the tunneling rate is parameterized according to the theory of Janev et al. A simple interpretation is given.     

Relativistic corrections to electron scattering by 2H, 3He,and 4He

Relativistic corrections to the scattering of electrons by a nonrelativistic nucleus are calculated, using the method of Close and Copley, and Krajcik and Foldy. Particular attention is paid to the deuteron, ³He and ⁴He. It is found that these corrections are substantially the same as those calculated by F. Gross for the deuteron. The corrections to ³He have the effect of moving the diffraction minimum, as calculated in a nonrelativistic model, outward by as much as 0.32 fm^?2. Smaller corrections are found for ⁴He.     

Absolute Electron Impact Cross Sections for Single Ionization of Metastable Atoms of H,He, Ne,Ar, Kr,Xe and Rn

Cross sections for single ionization of metastable atoms of H, He, Ne, Ar, Kr, Xe and Rn by electrons with impact energy E (threshold < E < 200 eV) are determined using a recently developed semiclassical formula. The formula consists of an energy dependent term (classical binary encounter approximation) and a term containing the weighted sum of the squared radii of maximum charge density of the outer electron subshells (Born Bethe approximation). Although this formula was originally devised and applied for ground state atoms, a comparison of the present calculations with previous calculations and measurements indicates that this formula can also be used successfully in case of metastable atoms.     

Ionization of metastable H(2S) atom by electron and positron impact

Summary Triple differential cross-section (TDCS) of hydrogen atom in its metastable (2S) state is studied theoretically by electron and positron impact for coplanar and asymmetric geometry. The final-state wave function in the present model satisfies the asymptotic boundary condition for asymmetric geometry (i.e. fork ₁≫k ₂). In the absence of experiment, present results are compared with other existing theoretical results. Apart from the double-peaked structure of the TDCS as in ground-state ionization, some interesting secondary structures are found, in conformity with other theories for ionization from 2S state.     

Screening effects in secondary electron production by equal velocity H+, H+2, He+, He++ions

Electron spectra produced by equal velocity (0.75 MeV/amu) H⁺, H⁺₂, He⁺ and He ⁺⁺ ions are shown. Screening effects are observed for He⁺ ions but not for H⁺₂. He⁺⁺ cross sections scale like Z² = 4 when compared to H⁺ cross sections.     

低能He~(2+)与He原子碰撞转移电离出射电子能谱研究

利用反应显微成像谱仪对70和100keV He2+与He原子碰撞转移电离(TI)过程中不同出射角度的电子能谱进行了测量,观测到出射电子能谱具有如下分布特征:出射电子速度分布介于0和入射离子速度vp之间;在不同出射角度电子能谱分布均有一极大值存在,随着出射角度的增大,能谱分布极大值逐渐减小;当电子出射角度等于45°时,多数电子集中在0eV附近。上述特征可由低能离子-原子碰撞"准分子"模型进行定性解释。在100keV He2+-He转移电离出射电子能谱中有靶电子被俘获至散射离子连续态(electron capture to continuum,简称ECC)电子的贡献,这可看做是动力学两步过程的作用。     

Large-space cluster model calculations for the 3He(3He,2p)4He and 3H(3H,2n)4He reactions

The ³He(³He,2p)⁴He and ³H(³H,2n)su4He reactions are studied in a microscopic cluster model. We search for resonances in the ³He+³He and ⁴He + p + p channels using methods that treat the two- and three-body resonance asymptotics correctly. Our results show that the existence of a low-energy resonance or virtual state, which could influence the ⁷Be and ⁸B solar neutrino fluxes, is rather unlikely. Our calculated ³He(³He,2p)⁴He and ³H(³H,2n)⁴He cross sections are in a good general agreement with the experimental data.     

Nightside Martian Ionosphere Produced by Electron Impact Ionization

Based on the Martian magnetic field model established by magnetohydrodynamics simulation, we determine the possible precipitation areas of the solar wind electron in the nightside Martian atmosphere, and analyze the electron impact ionization to estimate the height of the nightside Martian ionospheric peak and the electron density profile using the energy flux analysis method. The influences of the single electron energy, electron energy density and ionization efficiency on the altitude of the ionospheric peak and the electron density profile are also investigated. Our results show that the solar wind electron moves along the V-shaped solar wind magnetic field lines, to precipitate into the Martian atmosphere. Due to the crustal magnetic field, the precipitation regions on the nightside are quite narrow and unstable. The impact ionization happens at the altitude of 130-500km, and the height of the ionospheric peak is around 170km, with a peak electron density of 3.0×10^3 cm^-3. The simulation results are consistent with the results from Mars 4/5 and Viking occultation measurements.     

Microscopic study of the low-energy3He(3He, 2p)4He and3H(3H, 2n)4He fusion cross sections

We have calculated the³He(³He, 2p)⁴He and³H(³H, 2n)⁴He reaction cross sections at low energies within the microscopic multichannel resonating group method. For both reactions, we find good agreement with experiment. For the³H(³H, 2n)⁴He reaction, our calculated energy dependence reproduces that of each individual low-energy experimental data set, except for a normalization constant. Using this fact, we derive at a low-energy³H(³H, 2n)⁴He rate by taking the averaged mean of these fits.This work has been supported in part by the National Science Foundation, Grants PHY86-04197 and PHY88-17296.     

Ionization of O2 by metastable He(23 S, 21 S) at thermal collision energy

We investigate Penning ionization of O₂ by He(2³ S, 2¹ S) by means of electron spectroscopy. We give a detailed analysis of the reaction mechanism which completes and partly corrects earlier interpretations given by other authors. It becomes apparent that symmetry properties of the reaction partners play an important role.     

The (p, 2p) reaction on 2H, 3He and 4He

The (p, 2p) cross sections on ²H, ³He and ⁴He were measured at 65, 85 and 100 MeV. The experimental data show rather strong energy and target mass dependence, particularly for ⁴He.     

Collision-induced fundamental band of H2 in H2He and H2Ne mixtures at different temperatures

The collision-induced fundamental infrared absorption band of hydrogen in binary mixtures H₂He and H₂Ne at 77, 195, 273, and 298 K has been studied with absorption path lengths of 27 and 105 cm for gas densities up to 530 amagat for several base densities of hydrogen. In each of these mixtures the enhancement absorption profiles show, in addition to the usual splitting of the Q branch into the main Q_P and Q_R components, a splitting of the S(1) line into the S_P(1) and S_R(1) components at all the experimental temperatures and a secondary splitting of the main Q_P component into the Q_P(3) and Q_R(3) components at 273 and 298 K. The profiles of H₂He at 77 K also show a splitting of the S(0) line into S_P(0) and S_R(0). Integrated absorption coefficients were measured and binary and ternary absorption coefficients were derived. Van Kranendonk's theory of the ‘exponential-4’ model for the induced dipole moment was applied to the experimental binary absorption coefficients. The quadrupolar parts of these coefficients were calculated from the known molecular parameters and were then subtracted from the experimental values to obtain the overlap parts. The overlap parameters λ and ρ, giving respectively the magnitude and range of the overlap moment, were determined for each of the mixtures by obtaining the best fit of the calculated overlap part of the binary absorption coefficient as a function of temperature to the experimental values of the overlap parts. The values of λ, ρ, and μ(σ) (the overlap induced dipole moment at the Lennard-Jones intermolecular diameter σ) are as follows:

     

17.

Luminescent collisions of He+ and He++ ions with H2 molecules at energies below 2 keV     

B. Pranszke  S. Werbowy  R. Miotk  K. J. Borkowski  A. Kowalski 《The European physical journal. Special topics》2013,222(9):2309-2315

Spectroscopic studies of collisions between He⁺ and He⁺⁺ ions with H₂ gas target have been performed in the 200–600 nm wavelength range. Atomic lines of hydrogen Balmer series and several helium lines were identified and their excitation functions between 50 eV and 1 keV (2 keV for He⁺⁺) were determined.     

18.

Differential Double Ionization of He by Compton Photons and Charged Particles at Large Energy Transfers     

Wang J  McGuire JH  Burgdörfer J  Qiu Y 《Physical review letters》1996,77(9):1723-1726

     

19.

电子原子碰撞K壳层电离截面研究(英文)   总被引：1，自引：0，他引：1  

安竹  刘慢天  唐昶环  付玉川  彭秀峰  何福庆  罗正明 《原子核物理评论》2003,20(4):268-276

     

20.

Asymptotic interaction between He,H, H2 and a graphite surface     

G. Vidali  Milton W. Cole  C. Schwartz 《Surface science》1979,87(1):L273-L277

An atom or molecule far from a surface experiences an interaction V ~ ?C₃z^?3, where z is the distance to the surface. We compute the coefficient C₃ for He, H, and H₂ interacting with a graphite surface. The calculation utilizes measured frequency dependent values of the polarizabilities and dielectric function. Comparison is made with C₃ values deduced from surface scattering and adsorption experiments.     

Mixture	λ	ρ	μ(σ)
H2He	5.6 × 10?3	0.24 Å	2.92 × 10?2ea0
H2Ne	9.0 × 10?3	0.29 Å	4.85 × 10?2ea0

Luminescent collisions of He+ and He++ ions with H2 molecules at energies below 2 keV

Spectroscopic studies of collisions between He⁺ and He⁺⁺ ions with H₂ gas target have been performed in the 200–600 nm wavelength range. Atomic lines of hydrogen Balmer series and several helium lines were identified and their excitation functions between 50 eV and 1 keV (2 keV for He⁺⁺) were determined.     

Asymptotic interaction between He,H, H2 and a graphite surface

An atom or molecule far from a surface experiences an interaction V ~ ?C₃z^?3, where z is the distance to the surface. We compute the coefficient C₃ for He, H, and H₂ interacting with a graphite surface. The calculation utilizes measured frequency dependent values of the polarizabilities and dielectric function. Comparison is made with C₃ values deduced from surface scattering and adsorption experiments.