Electron Impact Excitation of 4p5 5p Levels of Krypton Atom from Metastable States

Optics and Spectroscopy - Data on electron impact excitation cross sections of the 4p55p levels of krypton from metastable states 4p55s3P0,2 have been obtained. They reflect the aggregate result of...     

Relaxation Processes at High Levels of Vibrational Excitation of Polyatomic Molecules in the Ground Electronic State

By the spectral and kinetic characteristics of the luminescence of vapors of polyatomic molecules (anthracene, anthraquinone, fluorenone) initiated by selective IR multiphoton excitation (IR MPE) of molecules in the ground electronic state S ₀ the relaxation processes proceeding under vibrational excitation of molecules to energies exceeding the energies of the lower excited electronic states have been investigated. The changes in the spectral and kinetic characteristics with increasing CO₂ laser energy density and vapor P _v and foreign gas pressure P _FG are analyzed. They are similar to the characteristics obtained for normal fluorescence of these molecules with changing vibrational energy E _vib content. On the basis of experimental data and model calculations it has been concluded that at the laser radiation densities used in the case of IR MPE the molecules reach energies considerably exceeding the energies of the electronic levels. It is shown that a nonadiabatic connection between the electronic states leads to the population of mixed electronic states isoenergetic to the vibrational levels of the ground electronic state and to emission of delayed luminescence spectrally identical to the normal luminescence of these molecules. It has been found that when high vibrational levels are populated, new relaxation channels, such as reverse electron relaxation, emission from high vibrational levels of the ground electronic state, and multiquantum vibrational energy transfer at collisions leading to a rapid establishment of vibrational equilibrium become important.     

Ca原子4s2-4s4p电子碰撞激发特性

基于全相对论扭曲波（RDW）电子碰撞激发计算程序REIE06,系统计算了Ca原子基态3p64s2 1S0到激发态3p64s4p 3P0,1,2 1P1精细结构能级的碰撞截面,总结了在不同入射电子能量下碰撞截面的变化规律。目前计算中,细致考虑了电子关联效应和Breit相互作用,计算结果与已有的理论计算进行比较,对实验值的相对误差较小。     

Ca原子4s~2-4s4p电子碰撞激发特性

基于全相对论扭曲波电子碰撞激发计算程序REIE06,系统计算了Ca原子基态3p~64s~(21)S_0到激发态3p~64s4p~3P_(0,1,2)~1P_1精细结构能级的碰撞截面,总结了在不同入射电子能量下碰撞截面的变化规律.目前计算中,细致考虑了电子关联效应和Breit相互作用,计算结果与已有的理论计算进行比较,对实验值的相对误差较小.     

Polarization of Radiation Emitted after Electron Impact Excitation

A programme is developed to calculate the polarizations of the radiation emitted after electron impact excitation. The fully relativistic distorted-wave method is used in cross-section calculations. The programme is applied to He- and Li-like ions. The calculated values of line polarization are compared with other theoretical results and experimental values. For He-like U, at lower incident energy, the present polarization agrees with the other theoretical ones within 1%, while at higher energy, the differences increase up to about 10%. For He-like Fe and Ti, the present results of polarization degree for most of the lines agree with the experimental data within the experimental error bars. For the Li-like Ti line q （ls2s2p^2p3/2 to ls^22s）, the present value of the polarization agree excellently with another theoretical one, and both the values are consistent with the measured data within the experimental error bar.     

Evolution of the magnesium surface during oxidation studied by Metastable Impact Electron Spectroscopy

The evolution of a polycrystalline magnesium surface during oxidation at room temperature has been studied by Metastable Impact Electron Spectroscopy (MIES). This technique allowed us to follow the metal-to-insulator transformation of the top layer of the surface. An electronic signal corresponding to a metallic behavior of the surface evidences the presence of under-stoichiometric MgO species on the surface. The total covering by oxygen of the Mg surface uppermost layer, obtained at around 10 L of oxygen deposition, does not correspond to a fully insulating surface. An insulating surface is obtained after 30 L of oxygen deposition. Depositions of CO₂ on a clean and a preoxidized polycrystalline Mg surface have been analyzed to give information about the composition of the surface and its evolution. CO₂ adsorption in the form of CO₃²⁻ compounds on preoxidized Mg is more efficient than on clean Mg. Oxygen species, corresponding to chemisorbed oxygen less bounded than oxygen in the MgO lattice, allows the formation of CO₃²⁻. Therefore, it is concluded that during oxygen deposition at room temperature, MgO islands and chemisorbed oxygen species coexist on the surface. Moreover, the larger the oxygen predeposition is, the less CO₃²⁻ compounds are formed, meaning a decrease of available chemisorbed oxygen sites. From oxidation measurements at high temperature (420 K), we show that MgO islands and uncovered Mg domain coexist. Further, no under-stoichiometric compound features have been observed. The high temperature allows the direct formation of oxide MgO species in islands.     

Fully RDWB for Electron Impact Excitation of Be-Like Neon

The collision strengths of Be-like neon ion for excitation from ground state 2s²(¹S₀) to nine excited states (principal quantum number n=2) by electron impact are presented.filly relativistic distorted-wave Born (RDWB) program [CHEN Guoxin, Phys. Rev. A53 (1996) 3227] is used for the calculations. Two transitions are compared with other's work. The rest seven transitions are predicted without other ROWB calculations. There are several detailed considerations in our procedures, so the present results should be reliable and accurate.     

利用飞行时间法测定锶原子5s5p3P1亚稳态能级寿命

本文结合TOF法和吸收光谱测量技术,利用连续光场测定了锶原子亚稳态能级的寿命。实验中,利用689nm激光连续泵浦基态锶原子至5s5p3P1亚稳态能级,然后在距泵浦区域不同距离处观测处于5s5p3P1态的原子对688nm探测光的吸收强度,得到锶原子5s5p3P1态的能级寿命,我们利用TOF法实验得到的能级寿命为21.9±0.8μs。本文给出的方法具备实验装置简单的优点,同时可获得较高的测量精度。     

A Numerical Calculation for Electron Impact Excitation of Copper

The scattering of electrons by atomic copper has been studied using Born approximation and the concept of the generalized oscillator strength (GOS). Differential and total cross-sections for the excitation of the 3d¹⁰ 4p² P state are calculated at incident energies of 100 eV and are compared with other available experimental and theoretical data. The agreement between our calculation for the differential cross-section and the available experimental results is fairly good at the forward angles, while the agreement at large angles is poor. The calculated total cross-sections are compared with the experimental data and those predicted by several theories. It is found that our calculation for the total cross-sections are in a good agreement with the close coupling calculation of Msezane and Henry (1986a, Physical Review A 33, 1631) for incident energies greater than 20 eV. The integrated cross-section measurements of Ismail and Teubner (1995, Journal of Physics B: Atomic, Molecular and Optical Physics 28, 4164) are in good agreement with the present calculation.     

Differential and Integral Cross Sections for Electron Impact Excitation of Lithium

The differential and integral cross sections for electron impact excitation of lithium from the ground state 1s22s to excited states 1s22p, 1s23l （l=s, p, d） and 1s24l （l=s, p, d, f）at incident energies ranging from 5 eV to 25 eV are calculated by using a full relativistic distorted wave method. The target state wavefunctions are calculated by using the Grasp92 code. The continuum orbitals are computed in the distorted-wave approximation, in which the direct and exchange potentials among all the electrons are included. A part of the cross sections are compared with the available experimental data and with the previous theoretical values. It is found that, for the integral cross sections, the present calculations are in good agreement with the time-independent distorted wave method calculation, for differential cross sections, our results agree with the experimental data very well.     

Xe I原子6s[3/2]2亚稳态寿命的理论研究

利用多组态Dirac Fock(MCDF)理论方法 ,系统地研究了延迟和相关效应对中性XeI原子5p56s[3/ 2 ]2—5p61S0 (M2 )辐射跃迁的影响 ,给出了亚稳态 6s[3/ 2]2的辐射寿命.与最新的磁光阱实验观测结果比较,目前的计算不仅大大提高了理论计算的精度 ,而且解释了实验和以往理论偏差非常大的原因. The recent high precision measurement on the lifetime of metastable 6s state of atomic xenon shows a difference with previous prediction by a factor of 2-3. In the present work, a new theoretical method which can systematically treat relaxation and correlation effects on the basis of the MCDF method is used to study the M2 transitions between the 5p 56s and 5p 6 configurations. By including the correlation contributions of the single and double excitations from the 5l subshells...     

Theoretical Study on Inner Shell Electron Impact Excitation of Lithium

Cross sections for electron impact excitation of lithium from the ground state 1s^22s to the excited states 1s2s^2, 1s2p^2, 1s2snp （n = 2-5）, 1s2sns （n = 3 5）, 1s2pns （n = 3-5）, and 1s2pnp （n = 3-5） are calculated by using a full relativistic distorted wave method. The latest experimental electron energy loss spectra for inner-shell electron excitations of lithium at a given incident electron energy of 2500 eV [Chin. Phys. Lett. 25 （2008）3649] have been reproduced by the present theoretical investigation excellently. At the same time, the structures of electron energy loss spectra of lithium at low incident electron energy are also predicted theoretically, it is found that the electron energy loss spectra in the energy region of 55-57eV show two-peak structures.     

Alpha Decay Half-Lives of Some Nuclei from Ground State to Ground State with Yukawa Proximity Potential

We study the half-lives of some nuclei via the alpha-decay process from ground state to ground state. To go through the problem, we have considered a potential model with Yukawa proximity potential and have thereby calculated the half-lives. The comparison with the existing data is motivating.     

Alpha Decay Half-Lives of Some Nuclei from Ground State to Ground State with Yukawa Proximity Potential

We study the half-lives of some nuclei via the alpha-decay process from ground state to ground state. To go through the problem, we have considered a potential model with Yukawa proximity potential and have thereby calculated the half-lives. The comparison with the existing data is motivating.     

Two Components of the Total Ionization Cross Sections of Atoms and Molecules by Electron Impact: Resonant Excitation and Decay of the Fermi Electron-Hole System and the Dipole Electron Transition from a Bound to a Free State at a Binary Collision

Large volume of the experimental data on the ionization cross sections of atoms and molecules by electron impact obtained by various authors using different methods is analyzed. The dependence of the ionization cross section Q on the energy of the incident electron E is described by a curve with a maximum. For E I, where I is the ionization potential, the cross section naturally vanishes. For E > I, it first increases fast, passes through a high maximum, and then monotonically decreases with increasing E. For comparatively large energies E > 100 I, the Bethe formula describes the experimental data almost exactly, but in the region of maximum I < E < 10 I, it deviates significantly from the measurement data. In the present paper it has been established that the experimental dependence Q(E) in the region of maximum is well described by a resonant curve similar to Lorentz distribution. It is assumed that the main contribution to the atomic ionization by a slow electron comes from the resonant excitation and the decay of the Fermi electron-hole system. An empirical formula for the cross section of atom ionization by electron impact Q(E) is suggested which takes into account resonance for incident electrons of small energies and is transformed into the Bethe formula for large E. The parameters of the formula for the ionization cross section are calculated by the least-squares method for H, He, Ne, Ar, C, N, O, Li, Na, H₂, N₂, O₂, K-shells of C, N, Ne, Ar, K, Ca, Rb, and Sr atoms and molecules. A comparison of the experimental dependences of the ionization cross section on the energy of the incident electron with the Bethe theoretical formula and empirical formulas suggested by Lotz, Alkhazov, Kim and Rudd, and Povyshev et al. demonstrates that the formula suggested in the present paper describes the available experimental data better than others.     

Minimizing the Ground State Energy of an Electron in a Randomly Deformed Lattice

We provide a characterization of the spectral minimum for a random Schrödinger operator of the form \({H = -\Delta + \sum_{i \in \mathbb{Z}^d}q(x - i - \omega_i)}\) in \({L^2(\mathbb{R}^d)}\) , where the single site potential q is reflection symmetric, compactly supported in the unit cube centered at 0, and the displacement parameters ω _i are restricted so that adjacent single site potentials do not overlap. In particular, we show that a minimizing configuration of the displacements is given by a periodic pattern of densest possible 2 ^d -clusters of single site potentials.The main tool to prove this is a quite general phenomenon in the spectral theory of Neumann problems, which we dub “bubbles tend to the boundary.” How should a given compactly supported potential be placed into a bounded domain so as to minimize or maximize the first Neumann eigenvalue of the Schrödinger operator on this domain? For square or rectangular domains and reflection symmetric potentials, we show that the first Neumann eigenvalue is minimized when the potential sits in one of the corners of the domain and is maximized when it sits in the center of the domain. With different methods we also show a corresponding result for smooth strictly convex domains.     

类镍Au~(51+)离子电子碰撞激发特性的研究

利用全相对论扭曲波方法和研究电子碰撞激发过程的计算程序REIE06系统计算了类镍Au~(51+)离子从基态(3s~23p~63d~(10))n=3壳层3 l(l=s、p、d)电子激发到4 l、5 l(l=s、p、d、f)的碰撞激发强度和截面,研究了在不同入射电子能量下截面的变化规律,通过对类镍Au51+离子涉及X射线激光跃迁的相关能级电子碰撞激发速率的计算,分析了等离子体中电子温度对碰撞过程的影响.部分计算结果与其它理论及实验结果进行了比较,取得了很好的一致性.     

类铜Au50+离子电子碰撞激发特性的研究

利用全相对论扭曲波（RDW）方法,系统计算了类铜Au50+离子的外壳层电子4s激发到4l 、5l （ l= s、p、d、f,除去4s-4s ）和内壳层电子3l （l = s、p、d）激发到4l 、5l （l = s、p、d、f）的碰撞激发截面,研究了在不同入射电子能量下截面的变化规律,给出了3d-4f 和3d-5f 精细结构能级的碰撞激发截面。部分计算结果与其它理论及最新实验结果进行了比较,取得了很好的一致性。