Experimental verification of a zero-dimensional model of the kinetics of XeCl* discharges by Xe*-, Cl*-, Ne*-, and H*-density measurements

Absorption spectroscopic measurements of effective particle number densities of excited Xe, Ne, Cl, and H performed on a small scale discharge with well-defined current and voltage pulses are compared with the results of model calculations over a wide range of discharge parameters. The reaction kinetic pathways determining the ionization and dissociative attachment rates have been verified by the good agreement obtained during the quasi-steady-state phase of the discharge for Xe and H. To reproduce the rise times of the excited Xe particle number densities during the ignition phase, the electron collision excitation cross sections of ground state Xe published by Puech and Mizzi [1] had to be enhanced by about 25%. From the Ne measurements it is concluded that the electron collision excitation cross sections of ground state Ne published by Puech and Mizzi [1] may be too large near the threshold. Measurements of excited Cl particle number densities are unsuitable to check the attachment kinetics of HCl, because these densities are mainly determined by reactions not involving the formation of Cl^– ions.     

势垒高度对Cl+H2(D2)反应的影响

使用三维含时波包方法在两个势能面上研究了Cl+H2(D2)反应．所使用的两个势能面都是从CW(Capecchi和Wener)势能面得到的，第一个是CW势能面的基态面加自旋轨道耦合修正，第二个是CW势能面的基态面没有自旋轨道耦合修正．在这两个势能面上得到了碰撞能从0.1到1.4 eV的积分截面以及反应几率．对于Cl与D2反应，考虑自旋轨道耦合后由于势垒高度的增加反应截面向高能处有一个平移，但Cl与H2反应在低能处的反应活性反而增大了，原因是虽然自旋轨道耦合效应增加了势垒高度，同时减小了势垒宽度，隧道效应更加明显，而隧道效应在低能处起着比较重要的作用，所以反应活性比较大．当碰撞能大于0.7 eV时，没有考虑自旋轨道耦合时势垒高度较低，因而反应活性较大．     

Vlasov-kinetic computer simulations of electrostatic waves in dusty plasmas: an overview of recent results

We have performed calculations for collisions between fully stripped ions, C⁶⁺ and N⁷⁺, and atomic hydrogen, in both its ground and first excited energy levels. We have employed the Classical Trajectory Monte Carlo method to obtain total ionization and charge exchange cross sections and state selective charge exchange cross sections in the 5–500 keV/amu energy range.     

Empirical photoabsorption cross sections for C,N, O,F and Cl obtained from molecular measurements between 50 and 340 Å

For many years, it has been known that many molecular photoabsorption cross sections in the hard X-ray region could be approximately obtained by summing the individual contributions of each atom to the total cross section. This article reports on an attempt to express 15 molecular cross sections as sums of empirical atomic cross sections for five constituent atoms C, N, O, F and Cl. For most wavelength ranges, the empirical atomic cross sections generated from a best fit to the molecular data were capable of describing the measured molecular cross sections to within 2% accuracy. In the 260–300 Å region where broad structures occur in the molecular spectra, the above model was slightly worse, perhaps indicating the appearance of molecular resonance effects discussed by other authors. It is suggested here that sums of empirical atomic cross sections will provide a useful means for prediction of molecular photoabsorption cross sections for molecules other than those investigated here for this limited wavelength region although it is acknowledge that the theoretical basis for this procedure is questionable.     

Mirroring doubly excited resonances in argon

New features are revealed in the low-energy photoionization spectrum of Ar by critically combining high photon resolution and differential photoelectron spectroscopic techniques. Two LS-forbidden doubly excited resonances are seen in the 3p(-1)(3/2, 1/2) partial cross sections which exhibit mirroring profiles, resulting in complete cancellation in the total photoionization cross section, as was predicted by Liu and Starace [Phys. Rev. A 59, R1731 (1999)]. These results demonstrate that a new class of weakly spin-orbit induced, mirroring resonances should be observable in partial, but not in total, collisional cross sections involving atoms, molecules, and solids in general.     

Rb(7S-5D)-H2,He能量转移截面与温度的关系

脉冲激光双光子激发Rb(5S)态到Rb(5D)或Rb(7S)态,在样品池条件下,利用原子荧光光谱方法测量了Rb(7S-5D)-H2,He碰撞能量转移截面与池温的关系.利用三能级模型的速率方程分析.通过测量在不同H2或He密度下的直接荧光与转移荧光的时间积分强度比,在353～493 K温度范围内得到了Rb(7S-5D)-H2,He的反应与非反应碰撞能量转移截面.对于Rb(7S)+H2→Rb(5D)+H2,其转移截面随温度的增加而减小,而其逆过程的转移截面则随温度的增加而增加.对于与He的碰撞,在不同温度下7S-5D的转移截面均符合细致平衡原理,7S,5D态与H2的碰撞速率系数是反应与非反应速率系数之和,利用实验数据可以分别确定反应与非反应截面,7S态的平均反应截面与5D态平均反应截面之比约为1.5.Rb(7S)与H2的反应活动性大于Rb(5D).     

Influence of radiation cross section uncertainties on shock wave structure

This numerical study investigates the sensitivity of non-equilibrium shockwave structure to uncertainties in (a) the ground and excited state continuum radiative cross section and (b) the bound-bound radiative cross section in a three level (ground, excited, and free electronic states considered) argon-like gas at Mach 18 and a pressure of 1 cm Hg. Changing the values of the radiative cross sections by an order of magnitude does not significantly influence the relaxation region; however, a large change occurs in not only the magnitude but also the extent of both the electron and excited state precursors. Increasing either the ground state continuum or the bound-bound cross section decreases the number of free electrons in front of the shock wave. These cross sections also influence the extent of the electron precursor through their influence on the ratio of the electrons produced by ground state photoionization to those produced by ground state photoexcitation followed by excited state photoionization. The bound-bound cross section also controls the excited state precursor, because the production of excited states is entirely due to line radiation. Increasing the excited state photoionization cross section increases both the magnitude and extent of the electron precursor, because the cross section influences the ratio of the two processes that compete to produce free electrons, and at the same time it influences the magnitude of the excited state precursor.     

Quantum theory of electron stimulated desorption

The process of electron stimulated desorption of adsorbates from metal surfaces is investigated within the framework of quantum mechanical scattering theory. The Born-Oppenheimer adiabatic approximation is assumed to be valid for the adsorbate motion. The transition amplitude for desorption via the resonant excitation of excited states of the adsorbate then can be factorized into an electronic excitation amplitude and a Franck-Condon factor. The Franck-Condon factor is more complicated than in molecules. The continuum of substrate excitations coupling to the adsorbate gives rise to an absorptive part of the Born-Oppenheimer potential governing the motion of the adsorbate in the excited state. This absorptive part leads to a considerable reduction of the desorption cross section. Explicit quantum mechanical expressions for the corresponding reduction factor are given.The desorption of neutrals is considered in some detail. It turns out that within the adiabatic approximation this process requires the existence of neutral excited states of the adsorbate. The reneutralization of ionic excited states by electron capture from the substrate back into the ground state of the adsorbate, while possible on purely energetical grounds, occurs with zero probability in the adiabatic approximation and thus cannot be responsible for the large abundance of neutral desorbing particles. Neutral excited states of the adsorbate in principle should show up in inelastic electron scattering. The relation between electron stimulated desorption cross sections and inelastic electron scattering cross sections is discussed briefly.     

Experimental study on the system of Cl/Cl_2/He/HN_3/I_2

Using a microwave generator, chlorine diluted by helium was dissociated to chlorine atoms that subsequently reacted with hydrogen azide to produce the excited states of NCl(a1△). Meanwhile, molecular iodine with carrier gas of helium reacted with atomic chlorine to produce atomic iodine which then was pumped to excited state of I(2P1/2) by an energy transfer reaction from NCl(a1△). In this paper, the changes of NCl(a1△) and NCl(b1∑) emission intensity is presented when I2/He is introduced into the stream of Cl/Cl2/He/HN3/NCl(a1△)/NCl(b1∑). The dependences of atomic iodine I(2P1/2) on flow rates of gases were also investigated. The optimum parameters for I(2P1/2) production are given.     

Importance of Relativistic Effects for Intermediate-Z Elements： Photoionization Process of Excited Na

Using a modified R-matrix code, the fine-structure-resolved partial photoionization cross sections of excited Na （Z = 11） are calculated within the Breit-Pauli approximation. Our calculated energy levels of Na＋ and Na are in good agreement with the experimental values within 1% and the branching ratios of the J-resolved partial cross sections are consistent with the recent measurements within the experimental uncertainties. The agreements are impossible to be obtained without adequately taking into account the relativistic effects and the electron correlations together. Therefore, even for the intermediate-Z elements （e.g. Na with Z = 11）, the relativistic effects （mainly the spin-orbit interactions） should not be neglected.     

Collisional and radiative processes with participation of highly excited states of atoms and molecules

A number of processes in which highly excited states of atoms and molecules participate are investigated. These processes are of interest for the kinetics of a low-temperature plasma, for atomic and molecular spectroscopy, and for astrophysics. A quasiclassical theory is developed for transitions between Rydberg states with change of the principal quantum number, and also for the processes of direct and associative ionization of highly excited atoms, which result from collisions between a neutral particle and its atomic core. The state of the inner electrons of a quasimolecular (molecular) ion is not altered by transitions of the outer electrons. Specific calculations are carried out for the case of the collision of hydrogen H(n) with helium He (1s²) atoms. It is shown that the cross sections and the rate constants of these processes are determined in this case by the mechanism investigated in the paper, and not by scattering of the Rydberg electron by the neutral particle. The cross sections for dipole excitation and dissociation of molecular ions from high vibrational energy levels by electron impact is calculated in the Born-Coulomb approximation. The cross sections and the rates of dissociative and three-particle attachment of electrons to ions are determined. The processes of autoionization and autodissociation decay of Rydberg states of vibrationally excited molecules are determined. Also investigated are radiative transitions near the dissociation limit of diatomic molecular ions and neutral molecules, viz., photodissociation and radiative decay of high vibrational levels, and photodissociation and translational (inverse-bremsstrahlung) absorption in collision of atomic particles.Translated from Trudy Ordena Lenina Fizicheskogo Instituta im. P. Lebedeva AN SSSR, Vol. 145, pp. 80–130, 1984.     

Photoabsorption cross sections for chlorinated methanes and ethanes between 46 and 100 Å

Photoabsorption cross sections for the methanes CCl₄, CCl₃F, CCl₂F₂, CClF₃, CF₄, CHClF₂, CHCl₂F and the ethanes C₂F₆, C₂ClF₅, C₂Cl₂F₄ were measured between 46 and 100 Å. In particular, the 0.2 Å resolution provides some insight into the Cl 2p absorption process. It is noted that the molecular cross section for all 8 Cl-containing gases display an L edge “discontinuity” of 3.55±0.15 Mb per Cl atom. The experimental molecular cross sections are compared with sums of atomic cross sections at 100 Å using both theoretical and empirical atomic values. The sums of theoretical atomic cross sections describe every experimental molecular value to better than 10%. The sums of empirical atomic cross sections describe molecular values to within 2%.     

Substrate-induced spin-orbit splitting of quantum-well and interface states in Au,Ag, and Cu layers of different thicknesses on W(110) and Mo(110) surfaces

The substrate-induced spin-orbit splitting of interface and quantum-well states formed in Au, Ag, and Cu layers on W(110) and Mo(110) surfaces has been revealed using angle- and spin-resolved photoelectron spectroscopy. It has been shown that the magnitude of the splitting depends noticeably on the atomic number of the substrate material and is markedly larger for layers of these metals on W(110), i.e., on the surface of a metal with a larger atomic number (Z _W = 74), than on the surface of Mo(110), i.e., an element with a smaller atomic number (Z _Mo = 42), while depending only weakly on the atomic number of the adsorbed metal. Measurements of the dispersion of the formed quantum-well states have shown that the substrate-induced spin-orbit splitting increases with increasing parallel component of the photoelectron momentum (which correlates with the Rashba model) for all thicknesses of deposited films (up to 10 ML). The magnitude of induced spin-orbit splitting of the interface states evolving in monolayer Au, Ag, and Cu coatings on W(110) and Mo(110) decreases with increasing parallel component of the excited photoelectron momentum.     

New ab initio Potential Energy Surfaces for Cl(2P3/2, 2P1/2)+H2 Reaction

采用多参考组态相互作用的计算方法和很大的基组构造了Cl+H₂反应体系的一组新的三维从头算势能面. 该势能面包含Cl+H₂体系的能量最低的三个绝热态,并在非绝热近似下转化为四个非绝热势能面. 另外,旋轨耦合矩阵元也基于Breit-Pauli Hamil-tonian计算得到. 对角化这四个非绝热势能和两个旋轨耦合矩阵元组成的全耦合Hamiltonian,得到了三个考虑旋轨耦合后的绝热势能面.基于这组新势能面的非绝热动力学计算结果与最新的实验符合得很好,很好地解释了     

Cl(2P)+D2→DCl+D反应中波恩-奥本海默近似有效性的交叉分子束研究

本文利用高分辨的里德堡态氘原子标识-交叉分子束装置,研究了碰撞能为4.5∽6.5 kcal/mol范围内Cl(²P)[Cl(²P_3/2)和Cl^*(²P_1/2)]与D₂的反应. 虽然自旋轨道激发态反应Cl^*(²P_1/2)+D₂在波恩-奥本海默(B-O)近似下本应是禁阻的,但实验中观测到了该反应的贡献. 通过测量靠近后向的碰撞能相关的微分散射截面连线,发现低碰撞能下的产物主要来自于B-O近似禁阻的反应Cl^*+D₂. 随着碰撞能的提高,自旋轨道基态反应Cl+D₂的反应性增加明显要比自旋轨道激发态反应Cl^*+D₂更快,并且在高碰撞能下成为产物的主要来源. 实验结果表明：在低碰撞能下,Cl^*中自旋轨道激发态的额外能量,可以帮助B-O近似禁阻的反应Cl^*+D₂越过势垒;然而当碰撞能接近和高于反应势垒时,B-O近似允许的反应Cl+D₂占主导地位. Cl/Cl^*+D₂反应中B-O近似有效性的特征与其同位素反应Cl/Cl^*+H₂是一致的.     

Electron Correlations,Spin-Orbit Coupling,and Antiferromagnetic Anisotropy in Layered Perovskite Iridates Sr_2IrO_4

The effects of electron correlations and spin-orbit coupling on the magnetic anisotropy in the antiferromagnetically ordered 5 d perovskite iridates Sr_2IrO_4 is investigated theoretically using a microscopic model includes a realistic five-orbital tight-binding Hamiltonian, atomic spin-orbit coupling, and multi-orbital Hubbard interactions. Hartree-Fock approximation is applied to obtain the ground state properties with varying spin-orbit coupling and electron correlations.We demonstrate that the interplay between the atomic intraorbital Coulomb repulsion and the Hund's rule coupling leads to a remarkable variability of the resulting magnetic anisotropy at a constant nonzero spin-orbit coupling. At the same time, the preferred direction of the ordered antiferromagnetical moment remains unaltered upon changes in the strength of spin-orbit coupling.     

Electron Correlations,Spin-Orbit Coupling,and Antiferromagnetic Anisotropy in Layered Perovskite Iridates Sr2IrO4

The effects of electron correlations and spin-orbit coupling on the magnetic anisotropy in the antiferromagnetically ordered 5d perovskite iridates Sr₂IrO₄ is investigated theoretically using a microscopic model includes a realistic five-orbital tight-binding Hamiltonian, atomic spin-orbit coupling, and multi-orbital Hubbard interactions. Hartree-Fock approximation is applied to obtain the ground state properties with varying spin-orbit coupling and electron correlations. We demonstrate that the interplay between the atomic intraorbital Coulomb repulsion and the Hund's rule coupling leads to a remarkable variability of the resulting magnetic anisotropy at a constant nonzero spin-orbit coupling. At the same time, the preferred direction of the ordered antiferromagnetical moment remains unaltered upon changes in the strength of spin-orbit coupling.     

Quantum theory of electron stimulated desorption

The process of electron stimulated desorption of adsorbates from metal surfaces is investigated within the framework of quantum mechanical scattering theory. The Born-Oppenheimer adiabatic approximation is assumed to be valid for the adsorbate motion. The transition amplitude for desorption via the resonant excitation of excited states of the adsorbate then can be factorized into an electronic excitation amplitude and a Franck-Condon factor. The Franck-Condon factor is more complicated than in molecules. The continuum of substrate excitations coupling to the adsorbate gives rise to an absorptive part of the Born-Oppenheimer potential governing the motion of the adsorbate in the excited state. This absorptive part leads to a considerable reduction of the desorption cross section. Explicit quantum mechanical expressions for the corresponding reduction factor are given.The desorption of neutrals is considered in some detail. It turns out that within the adiabatic approximation this process requires the existence of neutral excited states of the adsorbate. The reneutralization of ionic excited states by electron capture from the substrate back into the ground state of the adsorbate, while possible on purely energetical grounds, occurs with zero probability in the adiabatic approximation and thus cannot be responsible for the large abundance of neutral desorbing particles. Neutral excited states of the adsorbate in principle should show up in inelastic electron scattering. The relation between electron stimulated desorption cross sections and inelastic electron scattering cross sections is discussed briefly.On leave of absence from (present address) Physikdepartment der TUM, München-Garching and Max-Planck-Institut für Festkörperforschung, Stuttgart     

Analytical Expressions for the Differential Elastic Scattering Cross Sections of Nonidentical Nuclear Particles with Channel Spins 3/2 and 5/2

Russian Physics Journal - In this paper, general analytical expressions are obtained for the differential elastic scattering cross sections of two nuclear particles with allowance for spin-orbit...     

Elastic and inelastic scattering of 178 MeV protons from 58Ni and 60Ni

The elastic and inelastic scattering of 178 MeV protons from ⁵⁸Ni and ⁶⁰Ni has been studied. Angular distributions were measured for the differential cross sections for elastic scattering as well as inelastic scattering from excited states below about 5 MeV, all with natural parity. For the elastic and for the inelastic scattering from the first excited state (2⁺ in both nuclei, the angular distributions for the polarization were also measured. The measurements extend out to c.m. angles of about 60°, corresponding to a momentum transfer of about 600 MeV/c.The elastic and inelastic scattering data were compared to the results of coupled-channel calculations in the vibrational model using a deformed spin-orbit interaction of the full Thomas form. Good agreement was found in general showing that the main features of the experimental results are well described in this model.