L-shell ionization of atoms by relativistic electrons

A theoretical study of theL-shell ionization of atoms by relativistic electrons is made for atomic numbers in the range 47 to 92. A new potential model recently proposed by Das and Chakraborty dealing with atomic screening effect in a better way has been used. The results are in satisfactory agreement when compared with some available experimental results and also with the theoretical results of Scofield.     

Alpha particle and deuteron impactL-shell ionization of Ar,Cu, Ge,Br, Zr and Ag

Alpha particle and deuteron impactL-subshell ionization cross-sections of Ar, Cu, Ge, Br, Zr and Ag have been computed using Vriens’ expressions for ionization cross-section of atoms due to impact of heavy charged particles. The effects of Coulomb deflection of the projectile and increase in binding of the target electron in the presence of projectile have been incorporated. Hartree-Fock velocity distributions for the target electrons have been used in the present calculations. The simple binary encounter approximation model is found to give results which are in satisfactory agreement with those obtained from experiments and from other theories.     

氧离子轰击引起钽的L壳层X射线发射截面的研究

在北京原子能研究院串联加速器上,利用20—45 MeV的O⁵⁺轰击Ta靶,研究靶的L壳层X射线. 给出了Ta的L壳层各亚壳层Ll,Lα,Lβ和Lγ X射线发射截面的比值,并且与ECPSSR理论计算做了比较. 结果表明,在误差范围内比值σ(Ll)/σ(Lα)、σ(Lβ)/σ(Lα)和σ< 关键词： L壳层X射线')" href="#">L壳层X射线 发射截面 ECPSSR理论     

Measurements of K-shell ionization cross sections of35Br,37Rb,39Y using low energy protons

K-shell ionization cross section measurements are reported for₃₅Br,₃₇Rb and₃₉Y targets caused by protons over 300–400 keV energy range in 20 keV increment. The K-shell ionization cross sections (σ _k ^l ) at different energies were deduced from the K_α and K_β X-ray production cross sections which were obtained from X-ray yields of the K_α and K_β transitions. The experimental values are compared with the calculated values of ECPSSR theory and empirical reference cross sections. The resultant K-shell ionization cross sections are found to be in reasonable agreement with the ECPSSR theory. The K_α/K_β intensity ratios are also presented and compared with other experimental values and also with the theoretical one-hole values given by Scofield.     

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.     

L-subshell ionization cross sections for Au,Pb, and Bi by 60–600 keV electron impact

TheL ₁-,L ₂- andL ₃-subshell ionization cross sections of Au, Pb and Bi by 60–600 keV electron impact have been determined from the measured x-ray production cross sections. The experimental results have been compared with the relativistic PWBA, the Binary Encounter Approximation (BEA) and the Kolbenstvedt Approximation (KA) calculations. These calculations, especially the relativistic PWBA, give good agreement with the experimental data for theL ₃-subshell. For theL ₁- andL ₂-subshells there are some deviations and these can explain the disagreement observed for theL _α/L _χ- andL _γ/L _χ intensity ratios.     

Proton and α-particle impactM-shell ionization of atoms in binary encounter approximation

M-shell ionization cross sections for atoms due to the impact of proton and α-particles have been calculated in the binary encounter approximation. The effects of Coulomb deflection of the incident projectile and increase in binding of the target electron have been investigated. Roothan-Hartree-Fock velocity distribution for the target electrons has been used in the present work. The calculated cross-sections have been compared with experimental results and other theoretical calculations wherever available. The present calculations give a good account of experimental observations.     

Lifetime measurements of metastable states of Au,Bi, Cd,Mg, Pb,and Sr in an acetylene/air flame by laser-enhanced ionization spectrometry

The collisional dominated lifetimes of 9 metastable states of Au, Bi, Cd, Mg. Pb, and Sr in an acetylene/air flame have been measured by the step-wise delayed laser-enhanced ionization spectrometry technique. First, the dependency of the lifetime of the metastable 6p ^{2 3} P ₁ state in Pb upon both flame composition and height in the flame were studied. It was found that the lifetime was significantly shorter, both for lean as well as for rich flames, as compared to a stoichiometric composition. The lifetime was furthermore found to be dependent of the height in the flame with a maximum around 10 mm. The lifetimes were not significantly affected by the electron concentration in the flame. The lifetimes for the other metastable states were determined for one given flame composition ( 0.9 _stoich) and one given height (20 mm) only. The measured lifetimes were found to be between 5 ns and 3.1 s. The results show clearly that the lifetimes of metastable states are significantly shortened in the flame (as compared to natural lifetimes). The results also indicate that the metastable states which are of the same parity as the ground configuration (Au, Bi and Pb) in general have longer (collisional) lifetimes (85 ns to 3.1 s) than those which are forbidden to decay to the ground configuration only by violation of spin conservation (Cd, Mg and Sr) (5–33 ns).     

Resonant two-photon ionization and mass-analyzed threshold ionization spectroscopy of the selected rotamers of m-methoxyaniline and o-methoxyaniline

We report the resonant two-photon ionization and mass-analyzed threshold ionization (MATI) spectra of m-methoxyaniline and o-methoxyaniline. The vibronic features of m-methoxyaniline are built on 34308 ± 2 and 34495 ± 2 cm⁻¹ corresponding to the origins of the S₁ ← S₀ electronic transition (E₁’s) of the cis and trans rotamers. Analysis of the MATI spectra gives the adiabatic ionization energies (IEs) of 59983 ± 5 and 60879 ± 5 cm⁻¹ for these two species. o-Methoxyaniline is found to have only one stable structure whose E₁ and IE are 33875 ± 2 and 58678 ± 5 cm⁻¹, respectively. Most of the active vibrations of m- and o-methoxyaniline in the electronically excited S₁ and cationic ground D₀ states result from the in-plane ring vibrations. Comparing these data with those of p-methoxyaniline allows us to learn about the vicinal substitution effects resulting from the relative locations of the NH₂ and OCH₃ substituents.     

Evolution of emergent C-points, L-lines, and C-lines in free space

Polarization singularities,which emerge from the incoherent superposition of two vector electric fields with the same frequency,and their evolution in free space are studied analytically and illustrated by numerical examples.It is shown that there exist C-points,L-lines,in particular,C-lines in incoherently superimposed two-dimensional wavefields.Usually,the C-lines are unstable and disappear during the free-space propagation.The motion,pair creation-annihilation process of the emergent C-points,as well as the distortion of the L-lines may take place,and the degree of polarization of the emergent C-points varies upon propagation and may be less than 1.     

Theoretical study on K, L, and M X-ray transition energies and rates of neptunium and its ions

The transition energies and electric dipole （El） transition rates of the K, L, and M lines in neutral Np have been theoretically determined from the MultiConfiguration Dirac-Fock （MCDF） method. In the calculations, the contributions from Breit interaction and quantum electrodynamics （QED） effects （vacuum polarization and self-energy）, as well as nu- clear finite mass and volume effects, are taken into account. The calculated transition energies and rates are found to be in good agreement with other experimental and theoretical results. The accuracy of the results is estimated and discussed. Furthermore, we calculated the transition energies of the same lines radiating from the decaying transitions of the K-, L-, and M-shell hole states of Np ions with the charge states Np1＋ to Np6＋ for the first time. We found that for a specific line, the corresponding transition energies relating to all the Np ions are almost the same; it means the outermost electrons have a very small influence on the inner-shell transition processes.     

Calculated cross sections for the single ionization of atoms (N, Cu, As, Se, Sn, Sb, Te, I, Pb) by electron impact

By correcting some primary parameters in the semi-classical Deutsch--M?rk (DM) formula, this paper calculates the absolute single electron-impact ionization cross sections of atoms N, Cu, As, Se, Sn, Sb, Te, I and Pb from threshold to 10000eV. The calculated cross sections are compared with available experimental data and other theoretical results. An excellent agreement was achieved between the calculated and measured cross sections for these atoms over a wide range of impact energies.     

Enhancement in the photoluminescence of ZnS nanowires by TiO2 coating and thermal annealing

Influences of the TiO₂ coating and thermal annealing on the photoluminescence (PL) properties of ZnS nanowires were investigated. ZnS nanowires were synthesized by thermal evaporation of ZnS powder and then coated with TiO₂ by using the sputtering technique. The PL emission of ZnS nanowires can be significantly enhanced without nearly changing the wavelength of the emission by coating them with a TiO₂ layer with an appropriate thickness and then annealing them in an Ar atmosphere. The optimum TiO₂ coating layer thickness for the highest PL emission enhancement was found to be about 6.5 nm. The PL emission of the ZnS-core/TiO₂-shell coaxial nanowires is degraded by annealing in an oxygen atmosphere whereas it is enhanced by annealing in an argon atmosphere.     

A comparative study on geometries,stabilities, and electronic properties between bimetallic AgnX（X=Au,Cu;n=1-8）and pure silver clusters

Using the meta-generalized gradient approximation (meta-GGA) exchange correlation TPSS functional, the geo- metric structures, the relative stabilities, and the electronic properties of bimetallic Ag n X (X=Au, Cu; n=1–8) clusters are systematically investigated and compared with those of pure silver clusters. The optimized structures show that the transition point from preferentially planar to three-dimensional structure occurs at n = 6 for the Ag n Au clusters, and at n = 5 for Ag n Cu clusters. For different-sized Ag n X clusters, one X (X=Au or Cu) atom substituted Ag n+1 structure is a dominant growth pattern. The calculated fragmentation energies, second-order differences in energies, and the highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) energy gaps show interesting odd–even oscillation behaviours, indicating that Ag 2,4,6,8 and Ag 1,3,5,7 X (X=Au, Cu) clusters keep high stabilities in comparison with their neighbouring clusters. The natural population analysis reveals that the charges transfer from the Ag n host to the impurity atom except for the Ag 2 Cu cluster. Moreover, vertical ionization potential (VIP), vertical electronic affinity (VEA), and chemical hardness (η) are discussed and compared in depth. The same odd–even oscillations are found for the VIP and η of the Ag n X (X=Au, Cu; n=1–8) clusters.     

Effect of the reabsorption or radiation in the lines on the rate of ionization and recombination processes in a nonequilibrium plasma

To whom correspondence should be addressd.     

XF3 (X=N,P,As)价层电离势的运动方程耦合团簇理论计算

采用运动方程单双取代耦合团簇理论(EOM-CCSD)对XF₃(X=N,P,As)的价层垂直离势(VIP)进行了系统计算,同时对称匹配团簇组态相互作用(SAC-CI)、外价层格林函数(OVGF)以及部分三阶近似(P3)方法也被应用到目前计算.与已有的实验结果比较表明:EOM-CCSD计算的价层垂直电离势整体上与SAC-CI结果相近,而优于OVGF和P3理论结果,在整个价层上,EOM-CCSD结果与实验值总体差距约0.2 eV, 在外价层这种差距相对较小,在内 关键词： XF₃(X=N;P;As)')" href="#">XF₃(X=N;P;As) 垂直电离势 运动方程耦合团簇理论     

One-colour resonant two-photon ionization spectrum of the 1-fluoronaphthalene dimer and ab initio calculation

The one-colour resonant two-photon ionization(R2PI) spectrum of the 1-fluoronaphthalene(1FN) dimer has been studied in the wavelength range of 304 to 322 nm by using a supersonic molecular beam and time-of-flight mass spectrometry.Compared with the original band 00(at 313.8 nm) of the S1 ← S0 transition of the 1FN monomer,a red-shifted band was observed in the 1FN dimer spectrum at about 315 nm with a relatively large linewidth,nearly 2 nm.Based on the consideration of inductive effect and ab initio calculations,this red-shifted band is assigned to the first electronic excited transition of the 1FN dimer.A possible geometric structure of the 1FN dimer is also obtained with calculations that the two 1FN molecules are combined through two hydrogen bonds which are formed between the hydrogen atom of a molecule and the fluorine atom of a neighbouring molecule.A time-dependent calculation was also carried out and the results are consistent with the experimental data.     

Electronic properties and topological phases of ThXY(X= Pb,Au, Pt and Y= Sb,Bi, Sn) compounds

The electronic properties and topological phases of Th XY(X = Pb, Au, Pt, Pd and Y = Sb, Bi, Sn) compounds in the presence of spin–orbit coupling, using density functional theory are investigated. The Th Pt Sn compound is stable in the ferromagnetic phase and the other Th XY compounds are stable in nonmagnetic phases. Band structures of these compounds in topological phases(insulator or metal) and normal phases within generalized gradient approximation(GGA) and Engel–Vosko generalized gradient approximation(GGA EV) are compared. The Th Pt Sn, Th Pt Bi, Th Pt Sb, Th Pd Bi, and Th Au Bi compounds have topological phases and the other Th XY compounds have normal phases. Band inversion strengths and topological phases of these compounds at different pressure are studied. It is seen that the band inversion strengths of these compounds are sensitive to pressure and for each compound a second-order polynomial fitted on the band inversion strengths–pressure curves.