Coupled-channel optical calculation for positron—lithium scattering

Positron scattering with atomic lithium is investigated by using a coupled-channel optical method.The ionization continuum and positronium formation channels are taken into account via a complex equivalent-local optical potential.The positronium formation cross sections and the ionization cross sections,as well as the total scattering cross sections,are reported at energies above 3 eV and compared with available experimental and theoretical data.     

Electron-impact ionization cross section calculations for lithium-like ions

The electron-impact ionization of lithium-like ions C³⁺,N⁴⁺,O⁵⁺,Ne⁷⁺,and Fe2³⁺is studied using a combination of two-potential distorted-wave and R-matrix methods with a relativistic correction.Total cross sections are computed for incident energies from 1 to 10 times of ionization energy and better agreements with the experimental results are obtained in comparison with the theoretical data available.It is found that the indirect ionization processes become significant for the incident energy larger than about four times of the ionization energy.Contributions from the exchange effects along the isoelectronic sequence are also discussed and found to be important.The present method can be used to obtain systematic ionization cross sections for highly charged ions across a wide incident energy range.     

Elastic and inelastic positron-helium scattering

Elastic and inelastic positron--helium scatterings have been investigated with the coupled-channel optical method (CCO). Ionization continuum and positronium formation channels are included via a complex equivalent-local optical potential. Calculations are reported of cross sections of elastic scattering, total excitation and n=2, 3, and 4 excitations of ground-state helium for incident energies from 30~eV to 400~eV. The present calculation shows that the ionization and Ps-formation channels significantly affect the cross sections of elastic and inelastic positron--helium scatterings.     

J/ψ-J/ψ scattering cross sections of quadratic and Cornell potentials

We study the scattering of J/ψ - J/ψ mesons using quadratic and Cornell potentials in our tetraquark(cccc)system.The system’s wavefunction in the restricted gluonic basis,which is written by utilizing the adiabatic approximation and Hamiltonian,is used via a quark potential model.The resonating group technique is used to obtain the integral equations,which are solved to obtain the unknown inter-cluster dependence of the total wavefunction of our tetraquark system.T-Matrix elements are calculated from the solutions,and eventually,the scattering cross sections are obtained using the two potentials.We compare these cross sections and find that the magnitudes of scattering cross sections of quadratic potential are higher than the Cornell potential.     

Electron inelastic mean free paths in solids: A theoretical approach

In the present paper, the inelastic mean free path (IMFP) of incident electrons is calculated as a function of energy for silicon (Si), oxides of silicon (SiO2 ), SiO, and Al2O3 in bulk form by employing atomic/molecular inelastic cross sections derived by using a semi-empirical quantum mechanical method developed earlier. A general agreement of the present results is found with most of the available data. It is of great importance that we have been able to estimate the minimum IMFP, which corresponds to the peak of inelastic interactions of incident electrons in each solid investigated. New results are presented for SiO, for which no comparison is available. The present work is important in view of the lack of experimental data on the IMFP in solids.     

Resonance phenomena and threshold features in positron—helium scattering

Investigations of resonances and threshold behaviors in positron-helium scattering have been made using the momentum-space coupled-channels optical method.The positronium formation channels are considered via an equivalent-local complex potential.The s-wave resonances and the Wigner cusp feature at the positronium(n = 1) formation threshold are compared with the previous reports.The p-and the d-wave resonances and a Wigner cusp feature at the positronium(n = 2) formation threshold are reported for the first time.     

Photodissociation of sodium iodide and resonant ionization of sodium atom produced

Resonant ionization spectroscopy (RIS) and resonant ionization mass spectroscopy (RIMS) are employed to detect the photodissociation product of sodium iodide molecules in a molecular beam in an intense laser field in the absence of the buffer gases. Time of flight mass spectra is recorded. In particular, the appearances of multiphoton ionization are discussed.     

The theoretical and experimental investigations of Stark structure in sodium Rydberg states atoms

The experimental results of the Stark structure of Na in the vicinity of n~*=21-23 with the external electric field from 0 to 380V/cm are reported. The theoretical calculation of the stark levels of Na based on the atomic potential model are in good agreement with experiment. The limiting error between the theory and experiment turns out to be due to experimental uncertainty.     

Calculation of scattering parameters for ultracold ~6 Li-~7 Li elastic collisions

This paper theoretically studies the elastic scattering properties in a mixture of 6 Li and 7 Li atoms at cold and ultracold temperatures.Based on the constructed accurate interatomic potential of the triplet state for 6 Li 7 Li mixture by the mass scaling method,it calculates the interspecies s-wave scattering lengths and the p-wave scattering lengths by the variable phase method and the semiclassical method,respectively.The scattering length is in good agreement with the experiment.The partial-wave and total cross sections are also calculated and a rich resonance structure is found.     

Investigations on molecular constants of the CD（X^2∏） radical and elastic collisions between ground-state C and D atoms at low temperatures

The potential energy curve of the CD(X~2Π) radical is obtained using the coupled-cluster singles-doublesapproximate-triples [CCSD(T)] theory in combination with the correlation-consistent quintuple basis set augmented with diffuse functions,aug-cc-pV5Z.The potential energy curve is fitted to the Murrell-Sorbie function,which is used to determine the spectroscopic parameters.The obtained D0,De,Re,ωe,ωeχe,αe and Be values are 3.4971 eV,3.6261 eV,0.11197 nm,2097.661 cm 1,34.6963 cm 1,0.2083 cm 1 and 7.7962 cm 1,respectively,which conform almost perfectly to the available measurements.With the potential obtained at the UCCSD(T)/aug-cc-pV5Z level of theory,a total of 24 vibrational states have been predicted for the first time when J = 0 by solving the radial Schr¨odinger equation of nuclear motion.The complete vibrational levels,the classical turning points,the inertial rotation constants and centrifugal distortion constants are reproduced from the CD(X~2Π) potential when J = 0,and are in excellent agreement with the available measurements.The total and the various partial-wave cross sections are calculated for the elastic collisions between the ground-state C and D atoms at energies from 1.0×10 11 to 1.0×10 4 a.u.when the two atoms approach each other along the CD(X~2Π) potential energy curve.Only one shape resonance is found in the total elastic cross sections,and the resonant energy is 8.36×10 6 a.u.The results show that the shape of the total elastic cross section is mainly dominated by the s partial wave at very low temperatures.Because of the weak shape resonances coming from higher partial waves,most of them are passed into oblivion by the strong total elastic cross sections.     

Symmetric scattering in electron and positron impact ionization of metastable 2s-state hydrogen atoms

Triple differential cross sections for ionization of hydrogen atoms in the metastable 2s-state by the impact of electrons and positrons have been calculated for coplanar symmetric geometry. In this calculation a multiple scattering theory due to Das [10] and Das and Seal [11] has been used. An analysis of the results reveals that unlike scattering from the ground state, scattering from 2s-state is essentially a higher order process except for the binary collision direction. Moreover, here, the cross section results for 2s-state are much larger compared to those for scattering from the ground state. It is also found that the ionization mechanism at large scattering angles for ionization from the 2s-state is different from that for ionization from the ground state.     

Positron scattering from alkaline-earth elements

The total (elastic + inelastic) cross sections fore ⁺ impact on alkaline-earth elements from Be to Ra are calculated by employing a complex spherical optical potential. This potential has static, polarization and absorption components. The positron energy range is from a few eV to several thousand eV. We have compared our elastic cross sections for Mg and Ca with the other available results and the agreement is good for energies above 100eV. We have also compared our absorption cross sections withe ⁻ ionization cross sections at high energies where our absorption cross sections are in good accord. We have made Bethe plots fore ⁺ scattering on these elements.     

Positron scattering from hydrocarbons

The total cross sections for positron impact on hydrocarbons have been calculated using the additivity rule in which the total cross section for a molecule is the sum of the total cross section for the constituent atoms. The energy range considered is from a few eV to several thousand eV. The total cross sections for positron impact on an atom are calculated by employing a complex spherical potential which comprises of a static, polarization and an absorption potential. We have good agreement with the experimental results for hydrocarbons for positron energy ⩾100 eV. Our results also agree with the available calculations for CH₄ and C₂H₂ which employed full molecular wavefunctions beyond 100 eV. Our absorption cross sections also agree with molecular wave-function calculations for C₂H₂ and CH₄ beyond 100 eV. We have shown the Bethe plots fore ⁺−C ande ⁺−H scattering systems and Bethe parameters have been extracted. We have fitted the cross section for positron impact on hydrocarbons in the formσ _t(C _n H _m )=naE ⁻ b+mcE ⁻ d in the energy range 300–5000 eV wherea=195.0543,b=0.7986,c=371.1757 andd=1.1379 withE in eV andσ _t in 10⁻¹⁶ cm².     

Electron impact ionisation cross sections for atomic and molecular allotropes of phosphorous and arsenic

We report electron impact total ionisation cross sections for phosphorous (P), arsenic (As), diphosphorous (P₂), diarsenic (As₂), tetra phosphorous (P₄) and tetra arsenic (As₄) from the threshold of the target to 2000 eV. We employed spherical complex optical potential to compute total inelastic cross sections (Q_inel). The total ionisation cross section is extracted from the total inelastic cross section using the complex scattering potential–ionisation contribution method. The results of most of the targets studied here compare well with the measurements and the theoretical data wherever available. The correlation between the peak of ionisation cross sections with the number of target electrons and polarisability is also reported. It is observed that the maximum ionisation cross sections depend linearly on the number of target electrons and polarisability of the target. This linear correlation is used to predict the maximum ionisation cross sections for the targets (I₂, HI and PF₃) where no experimental data are available.     

He-HI复合物势能面及微分散射截面的理论研究

采用超分子单双迭代(包括非迭代三重激发)耦合簇理论CCSD(T)方法和由键函数3s3p2d1f组成的大基组, 计算得到了基态He-HI复合物相互作用的全程势能面. 该势能面上存在2个势阱, 分别对应于线性He-I-H和He-H-I构型, 势阱深度分别为4.473和2.996meV, He原子到HI分子质心的距离R分别为0.363和0.442nm. 使用Barker, Fisher和Watts提出的BFW势函数拟合计算得到的相互作用能数据, 获得了He原子与HI分子相互作用势的解析表达式. 在 关键词： He-HI复合物 势能面 微分散射截面     

正电子碰撞Ag，In，Sn原子L壳层电离截面的理论计算

在David Botz分析模型的基础上,综合考虑正电子及电子碰撞电离的库仑效应和电子交换效应,引入离子效应和相对论效应修正因子,计算了Ag,In,Sn原子的L壳层电离截面.计算结果表明,引入了修正因子的计算结果明显优于平面波波恩近似和扭曲波波恩近似的计算结果,并和最近文献的实验值符合得较好.其计算结果可为激光等离子体模拟提供准确参数.     

正电子碰撞Ag，In，Sn原子L壳层电离截面的理论计算

在David Botz分析模型的基础上，综合考虑正电子及电子碰撞电离的库仑效应和电子交换效应，引入离子效应和相对论效应修正因子,计算了Ag，In，Sn原子的L壳层电离截面.计算结果表明，引入了修正因子的计算结果明显优于平面波波恩近似和扭曲波波恩近似的计算结果，并和最近文献的实验值符合得较好.其计算结果可为激光等离子体模拟提供准确参数.     

Positron scattering by atoms

We describe the present status of coupled-state calculations for positron scattering by ‘one-electron’ atoms. We show how pseudostates are used to represent the continuum channels. Illustrative results from positron scattering by atomic hydrogen and the alkali metals are presented.