Relativistic Distorted-Wave Calculations of Electron Impact Excitation Cross Sections of Be-Like C2＋ Ions

A fully relativistic distorted-wave program is developed based on the Grasp92 and Ratip packages to calculate electron impact excitation （EIE） cross sections. As a first application of the program, the EIE cross sections of Be-like C^α＋ ions from the metastable 1s^22s2p^3 p to 1s^22p^2 ^3 p excitation and the inner-shell excitations are calculated systematically. Meanwhile, the correlation effects of target states are discussed. It is found that the correlation effects play an important role in the low energy EIE cross sections. An excellent agreement is found when the results are compared with previous calculations and recent measurements.     

BrCl分子近域轨道的电子动量谱学研究

Bromochlorodifluoromethane(CF2BrCl),also knownasHalon1211inindustry,isamainagent widelyusedforfiresuppressionapplicationsandhas receivedconsiderableattentionbecauseofitspotential forstratosphericozonedepletion[1,2].Thedetailed informationonpropertiesofCF2BrClmoleculesuchas ionizationpotential,chemicalbondingcharacterand electrondensitydistributionofmolecularorbitals,especiallyofthefrontiermolecularorbitals,isbelieved tobeimportantforchemicalreactionandpossible molecularrecognitionaccordingt…     

CFCl3分子2e和4a1轨道的电子动量谱研究

由于工业的迅速发展 ,使得空气质量急剧下降 ,因此对影响大气的分子进行深入研究变得非常必要 .本实验室已经对影响环境的甲烷[1] 、丙烷[2 ] 、CO2 [3] 等分子进行了电子动量谱研究 ,为环保提供了有用的数据 .CFCl3作为工业广泛应用的气雾剂和制冷剂原料 ,它的大量使用导致了大气中臭氧的减少[4 ] .前人已用光电子谱学的方法[5- 8] 研究了CFCl3,我们又用电子动量谱的手段对CFCl3分子进行了进一步的研究 ,即从波函数的层次上详细了解CFCl3的电子结构 .(e ,2e)电子动量谱学在研究分子的电子结构方面有非常独特的优越性[9- 12 ] ,它可以…     

Hyperspherical Calculations on Electron Affinity and Geometry for Li^- and Na^-

Using a model potential to describe the interaction between the core and the valence electron, we perform hyperspherical calculations for electron affinity and geometry of the weakly bound Li^- and Na^- systems. In our calculation, channel functions are expanded in terms of B-splines. Using the special properties of B-splines, we make the knot distributions more precisely, characterizing the behaviour of channel functions. This improves the convergence greatly. Our results are in good agreement with the other theoretical and experimental values.     

二氟甲烷分子3a1和2b2轨道的电子动量谱

借助电子动量谱学结合量子化学理论和其他方法可以给出轨道电子在整个空间的分布信息,由此给出电子运动的完备描述[1,2 ] .清华大学电子动量谱学实验室近几年已成功地对甲烷[3] 、异丁烷[4 ] 、环戊烷[5] 、二乙酰等[6 ] 分子的轨道电子动量分布进行了测量.我们利用第二代电子动量谱仪首次对CH2 F2 分子3a1和2b2 轨道的电子动量谱进行测量,并与理论计算结果作了比较.同时还计算了坐标空间和动量空间中电子在x - y平面的密度分布.电子动量谱学最基本的过程是(e ,2e)反应,即电子与靶粒子碰撞而发生的电离过程.而对于(e ,2e)反应,含有大量信…     

环己烯分子2b和3a轨道的电子动量谱学研究

报道了环己烯(C6H10)分子2b和3a轨道电子动量谱的首次研究,并且给出了价轨道的电离能谱信息,实验在非共面对称几何条件下的能量多道型电子动量谱仪下完成,入射电子的能量为1200eV加结合能.通过Hartree-Fock和密度泛函方法计算得到了C6H10分子2b和3a轨道的动量谱,在动量大于0.25a.u.区域理论与实验结果符合较好,实验结果与理论计算相比在低动量端出现“上翘”的现象,这可能是由于分子的扭曲波效应引起的.     

Electron impact ionization of SiCl<Subscript>2</Subscript> and SiCl

We measured absolute partial cross sections for the formation of all singly charged positive ions produced by electron impact on SiCl₂ and SiCl from threshold to 200 eV using the fast-neutral-beam technique. Some of the cross section curves exhibit an unusual energy dependence with a pronounced low-energy maximum at an energy around 30 eV, which may be indicative of the presence of indirect ionization channels. Dissociative ionization channels are dominant for both species. The experimentally determined total single ionization cross sections for both species agree very well with calculated cross sections using the Deutsch-M?rk (DM) formalism. A brief summary of the ionization cross sections determined for all four SiCl_x (x=1–4) species is given highlighting similarities and differences.     

Dielectronic Recombination of Sn^10＋ Ions and Related Satellite Spectra

Based on the multi-configuration Dirac-Fock method, theoretical calculations are carried out for the dielectronic recombination （DR） rate coefficients and the collision excitation rate coefficients of Sn^10＋ ions. It is found that the total DR rate coefficient has its maximum value between 10eV and 100eV and is greater than either the radiative recombination or three-body recombination rate coefficients （the number of free electrons per unit is 10^21 cm^3） for the ease of Te 〉 1 eV. Therefore, DR can strongly influence the ionization balance of laser produced multi-charged tin ions. The related dieleetronie satellite cannot be ignored at low temperature Te 〈 5 eV.     

Unified theory of bound and scattering molecular Rydberg states as quantum maps

Using a representation of multichannel quantum defect theory in terms of a quantum Poincaré map for bound Rydberg molecules, we apply Jung's scattering map to derive a generalized quantum map, that includes the continuum. We show that this representation not only simplifies the understanding of the method, but moreover produces considerable numerical advantages. Finally we show under what circumstances the usual semi-classical approximations yield satisfactory results. In particular we see that singularities that cause problems in semi-classics are irrelevant to the quantum map.     

Ab initio investigations on the electronic structure and optical properties of HX-ZnO

First-principles ultrasoft pseudopotential method is applied to study HX ZnO, which has a novel graphite like hexagonal structure transformed from wurtzite (WZ) phase under tensile stress along direction or compressive stress along [0001] direction. The electronic structure and optical properties, including dielectric function, reflectivity and absorption coefficient, of HX ZnO are calculated and compared with those of WZ ZnO under the given uniaxial stress. It is found that HX ZnO is an indirect semiconductor, being different from WZ ZnO. HX ZnO has a dielectric response different from WZ ZnO at ambient conditions or under the given uniaxial stress, especially in the case of E∥c. Similar variation is also observed in the reflectivity and absorption coefficient. The variation in the optical properties is attributed to the additional ZnO bond along c-axis HX ZnO.     

First-Principles Calculations for Structures and Melting Temperature of Si6 Clusters

We investigate the structures and the melting temperature of the Si6 cluster by using the first-principles pseudopotential method in real space and Langevin molecular dynamics. It is shown that the ground structure of the Si6 cluster is a square bipyramid, and the corresponding melting temperature is about 1923 K. In the heating procedure, the structures of the Si6 cluster change from high symmetry structures containing 5-8 bonds, via prolate structures containing 3-4 bonds, to oblate structures containing 1-2 bonds.     

Electron Scattering by C4H10 and C6H6 in the Energy Range 100--1000eV

We investigate the applicability of the independent atom model （IAM） to elastic electron scattering from complex polyatomic molecules, namely C4H10 and C6H6, in the energy range 100-1000eV. The cross sections of the elastic electron scattering are calculated by employing the IAM together with the relativistic partial waves. The incorporation of both the modified absorption potential and the extended structural factor in the IAM makes the elastic differential cross sections and momentum transfer cross sections have a good agreement with the available experimental data. The present simple model seems to be insensitive to the complexity of the target molecules so that the proposed procedure can be quite useful for calculation of electron scattering from bio-molecules.     

Effect of Ti doping on Ta2O5 stacks with Ru and Al gates

The Ti-doped Ta₂O₅ thin films (<10 nm) obtained by rf sputtering are studied with respect to their composition, dielectric and electrical properties. The incorporation of Ti is performed by two methods - a surface doping, where a thin Ti layer is deposited on the top of Ta₂O₅ and a bulk doping where the Ti layer is sandwiched between two layers of Ta₂O₅. The effect of the process parameters (the method and level of doping) on the elemental distribution in-depth of the films is investigated by the time of flight secondary ion mass spectroscopy (ToF-SIMS). The Ti and Ta₂O₅ are intermixed throughout the whole thickness but the layers are very inhomogeneous. Two sub-layers exist in all the samples — a near interfacial region which is a mixture of Ta-, Ti-, Si-oxides as well as TaSiO, and an upper Ti-doped Ta₂O₅ sub-layer. For both methods of doping, Ti tends to pile-up at the Si interface. The electrical characterisation is performed on capacitors with Al- and Ru-gate electrodes. The two types of MIS structures exhibit distinctly different electrical behavior: the Ru gate provides higher dielectric permittivity while the stacks with Al electrode are better in terms of leakage currents. The specific metal-dielectric reactions and metal-induced electrically active defects for each metal electrode/high-k dielectric stack define its particular electrical behavior. It is demonstrated that the Ti doping of Ta₂O₅ is a way of remarkable improvement of leakage characteristics (the current reduction with more than four orders of magnitude as compared with undoped Ta₂O₅) of Ru-gated capacitors which originates from Ti induced suppression of the oxygen vacancy related defects.     

Unique Magnetic Moment and Electronic Properties for Fe（MgO）n（n=1-8） Clusters： First-Principles Calculations

The geometries and electronic properties of Fe（MgO）n are systematically investigated by the density functional theory. The results show that the doped Fe atom is prone to bond with the O atom, and Fe almost does not disturb the frame of （MgO）n. The second-order energy difference, the fragmentation energies and the electron amnities show that Fe（MgO）4 and Fe（MgO）6 possess relatively higher stabilities. The HOMO-LUMO gaps of Fe（MgO）n decrease obviously as compared with （MgO）n. Almost equal unpaired electrons of the 3d state of the Fe atom in Fe（MgO）n result in a nearly equal magnetic moment of Fe（MgO）n.     

Experimental and theoretical analysis of the 5 pnpJ =0 e , 1 e , 2 e autoionizing spectrum of Sr

The even parity 5 pnpJ = 0, 1 and 2 doubly excited autoionizing states of strontium were investigated both experimentally and theoretically. Sr atoms in an atomic beam were excited through the two-step Isolated Core Excitation (ICE) scheme 5s^{2 1} S ₀ -λ ₁ → 5 sn'p ¹ P ₁ ( n' = 12-16)-λ ₂ → [5 p _3/2 np ] _J . The final ICE transition probes the [5 p _3/2 np ] _J resonances. However, the [5 p _1/2 np ] _J series below the 5 p _1/2 threshold were excited also due to their mixing with the [5 p _3/2 np ] _J perturbers. An extended energy region was covered below and above the 5 p _1/2 ionization limit by saturating the central ICE lobe and recording as many as possible “red” and “blue” secondary lobes. J identification was achieved by using mutually parallel and perpendicular linear polarizations of the laser beams. The ICE spectra were compared to those obtained by employing a two-step excitation scheme using the bound 4 d 5 p ¹ P ₁ valence state as an intermediate one. Final identification for very complex structures was achieved after comparison with theoretical energy level positions and excitation profiles produced by the R-matrix method combined with the multichannel quantum defect theory (MQDT) method. The agreement between theoretical and observed structures is quite satisfactory. Received 31 May 2000     

Ab Initio Calculations of Differential Cross Sections for Single Charge Transfer in ^3He^2＋ ＋ ^4He Collisions

The single charge transfer process in ^3He^2＋ ＋ ^4He collisions is investigated using the quantum-mechanical molecular- orbital close-coupling method, in which the adiabatic potentials and radial couplings are calculated by using the ab initio multireference single- and double-excitation configuration interaction methods. The differential cross sections for the single charge transfer are presented at the laboratorial energies E = 6 keV and lOkeV for the projectile ^3He^2＋. Comparison with the existing data shows that the present results are better in agreement with the experimental measurements than other calculations in the dominant small angle scattering, which is attributed to the accurate calculations of the adiabatic potentials and the radial couplings.     

Theoretical Study of Interesting Fine-Structure Splittings for 23P0, 1, 2 States along Helium Isoelectronic Sequence

Using the multi-configuration Dirac Fock method including the Breit interactions and QED corrections, we calculate the fine-structure energy levels of the 2^3 Po, 1,2 states along the helium isoelectronic sequence with atomic number up to Z = 36, where LS-coupling is appropriate. Our calculation results agree with the experimental results within about 1%. We elucidate the mechanism of the interesting fine-structure splittings for the 2^3Po,1,2 states along the helium isoelectronic sequence, i.e. the competitions between the spin-orbit interactions and the Breit interactions which represent the relativistic retardation effect of electromagnetic interactions.     

Application of R-matrix method to electron-H<Subscript>2</Subscript>S collisions in the low energy range

Electron-H₂S collision process is studied using the R-matrix method. Nine low-lying states of H₂S molecule are considered in the R-matrix formalism to obtain elastic integral, differential, momentum transfer and excitation cross sections for this scattering system. We have represented our target states using configuration interaction (CI) wavefunctions. We obtained adequate representation of vertical spectrum of the target states included in the scattering calculations. The cross sections are compared with the experiment and other theoretical results. We have obtained good agreement for elastic and momentum transfer cross sections with experiment for entire energy range considered. The differential cross sections are in excellent agreement with experiment in the range 3–15 eV. A prominent feature of this calculation is the detection of a shape resonance in ²B₂ symmetry which decays via dissociative electron attachment (DEA). Born correction is applied for the elastic and dipole allowed transition to account for higher partial waves excluded in the R-matrix calculation. The electron energy range is 0.025–15 eV.     

Electronic structure of Li3GaN2

First principles calculations, by means of the full-potential linearized augmented plane wave method within the local density approximation, were carried out for the electronic properties of Li₃GaN₂. The calculated lattice parameter is in good agreement with the measured one. The bandgap is direct at the Brillouin zone centre. The Li-N and Ga-N bonds are both ionic with a small covalent character of the latter one.     

Electron impact excitation of 2p and 3p states of hydrogen at intermediate energies

The recent theoretical work by Bartlett et al. [J. Phys. B 38, L95 (2005)] and the latest measurements on the reduced Stokes parameters , and for 54.4 eV electron impact excitation of the 2p state atomic hydrogen by Williams and Mikosza [J. Phys. B 39, 4113 (2006)] has motivated the present work. A coupled-channel-optical calculation with 9 and 12 atomic states supplemented with the continuum optical potentials for the stronger coupling channels has been performed. The calculated n = 2 and n = 3 differential cross sections and the reduced Stokes parameters are comparable with the state-of-the art calculations. There is closer agreement between the present calculations and the experimental measurements for the reduced Stokes parameters and in the n = 2p excitation at 54.4 eV. The present CCO calculations also display good accord with the limited experimental data for the reduced Stokes parameters in the n=3p excitation.