共查询到20条相似文献,搜索用时 0 毫秒
1.
David A.L. Kilcoyne C.M. McCarthy Sture Nordholm N.S. Hush P.R. Hilton 《Journal of Electron Spectroscopy and Related Phenomena》1985,36(2):153-185
A theory of molecular photoionization cross sections is developed on the basis of locally atomic character of the one-electron final state in the Golden Rule expression for the molecular orbital cross section. Ionization amplitudes from several atomic centres are added and rotationally averaged to produce molecular orbital cross sections displaying a sum of pseudo-atomic cross sections weighted according to the LCAO composition of the orbital and also two-centre products reflecting interference effects. The atomic ionization amplitudes are obtained by use of an atomic central potential constructed by an inversion procedure from the form of the ground state orbital. The theory is of a simple chemical nature but usually of at least semi-quantitative accuracy. In this work we illustrate the nature of the two-centre interference effects in small diatomic molecules (H2, HF, N2). 相似文献
2.
Sture Nordholm 《Journal of Electron Spectroscopy and Related Phenomena》1979,15(1):109-111
A new method for the calculation of quantum state decay rates, the absorbing boundary method (ABM), has recently been developed. In this talk the general form of the ABM will be outlined. The pseudo bound state approach to the calculation of continuum rates such as photoionization cross sections and used by Langhoff and coworkers will be briefly reviewed and shown to lack precision in the absence of information about the line widths and shapes of the pseudo bound states. It will then be noted that the ABM can be used to construct a rigorous new approach to the calculation of photoionization cross sections incorporating the necessary lifetime information for the pseudo bound states while still allowing the computation to be carried out by bound state procedures. 相似文献
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利用Dirac-Slater相对论自洽场理论,研究了入射光子能量较小时Na和K原子最外壳层电子的光电离截面的变化规律及其s和p壳层的Cooper最小,在论述Cooper最小的产生原因及其基本特征的基础上,分析了影响Cooper最小的主要因素原子实、主量子数、角量子数以及总量子数等,并对这种影响进行了较为详细的理论说明. 相似文献
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U. Heinzmann D. Schinkowski H. D. Zeman 《Applied Physics A: Materials Science & Processing》1977,12(1):113-113
The results of the measured absolute photoionization cross section from the 72
P excited states of cesium are reported. The following values have been obtained: (6.2±0.5)×10−18 cm2 and (8.8±1.6)×10−18 cm2 for the levels 72
P
1/2 and 72
P
3/2, respectively. 相似文献
6.
Sm和U原子光电离截面的模型势计算 总被引:1,自引:0,他引:1
本文给出了使用四种不同形式的势对Sm基态光学电子所属壳层光电离截面计算的结果,同时给出了U原子三个激发态参量形式的极化修正模型势光电离截面的计算结果.我们的结果与其他作者使用相同形式的势计算的结果较好地符合.使用参数形式的极化模型势计算光电离截面是一种有效的方法. 相似文献
7.
M. Ya. Amusia R. Krivec E. Z. Liverts V. B. Mandelzweig 《Journal of Experimental and Theoretical Physics》2006,102(4):556-561
We discuss the results of the calculation of the photoionization with deexcitation of excited He and helium-like ions Li+ and B3+ at high but nonrelativistic photon energies θ. Several lower 1
S and 3
S states are considered. We present and analyze the ratios R
d
+
* of the cross sections of photoionization with deexcitation, σ
(d)
+
*(θ), and of the photoionization with excitation, σ+*(θ). The dependence of R
d
+
* on the excitation of the target object and the charge of its nucleus is presented. In addition to theoretical interest,
the results obtained can be verified using long-lived excited states such as 23
S of He.
The text was submitted by authors in English. 相似文献
8.
利用相对论平均自洽场理论,研究了光电离截面在不同交换势下的差异,在对这种差异进行分析的基础上,对其变化规律做了较详细的理论说明.计算结果表明:光电离截面随交换系数的增大而增大;电子所感受到的平均核势场越小,交换势所起的作用则相对地有所增加,从而对光电离截面的影响更大. 相似文献
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V. A. Zilitis 《Optics and Spectroscopy》2006,101(5):661-665
The photoionization cross sections for the ground and some excited states of 11 ions of the rubidium isoelectronic sequence from Rb through Ag10+ are calculated by the relativistic Dirac-Fock self-consistent field method. The energy dependence of the photoionization cross sections and the changes in the threshold values along the isoelectronic sequence are considered. The influence of the exchange effect and the choice of gauge on the calculated values of photoionization cross sections is examined. For practical use, the calculated cross sections are approximated by an analytical expression. Along with the total photoionization cross sections, the asymmetry parameter in the angular distribution of photoelectrons and the degree of their polarization are also calculated. 相似文献
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Photoionization cross sections of lighter neutral elements (Na, K, Mg, C, N, O) have been calculated by means of the scaled Thomas-Fermi potential and compared with results obtained by other methods. In contrast to the quantum-defect method, the present method is applicable and yields reasonable results also for ultraviolet transitions, that is, for electron energies up to several Rydbergs and for low-lying bound states with large quantum defect. 相似文献
12.
Moshe Cohen Pinchas Mandelbaum 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2014,68(1):1-13
Detailed level-by-level calculations of cross sections and rate coefficients for electron impact direct ionization and excitation-autoionization of AsI-like ions in the 3d 104s 24p 3 (4S3/2) ground state have been performed. The cross sections are presented in the energy range near the threshold for the five ions Mo9+, Xe21+, Pr26+, Dy33+ and W41+. The rate coefficients are given for all the ions from Sr5+ to U59+ in the AsI sequence at the seven electron temperatures (k T e = 0.1E I ,0.3E I ,0.5E I ,0.7E I ,E I ,2E I and 10E I , where E I is the first ionization energy). The calculations include the contribution of direct ionization (DI) calculated using the Lotz formula approximation and the contributions of excitation-autoionization (EA) computed in the framework of the Distorted Wave (DW) approximation for the 4s ? nl, 3d ? nl and 3p ? nl resonant inner-shell excitations. The ionization enhancement due to the EA channels is presented as a function of Z along the AsI isoelectronic sequence. The present results show the great importance of the EA processes; an ionization enhancement factor of up to 6.5 is predicted for instance for Dy33+ (Z = 66) at electron temperature of coronal equilibrium maximum abundance. 相似文献
13.
Etienne Plésiat Piero Decleva Fernando Martín 《Central European Journal of Physics》2013,11(9):1157-1162
We use an extension of the static-exchange density functional theory (DFT) method, previously reported in [E. Plésiat et al., Phys. Rev. A 2, 023409 (2012), E. Plésiat, P. Decleva, F. Martín, Phys. Chem. Chem. Phys. 31, 10853 (2012)], to evaluate vibrationally resolved (total and angular) K-shell photoelectron cross sections of methane. The calculated cross sections are in very good agreement with the existing experimental measurements at low photoelectron energies. We show that, in contrast with the rich interference patterns previously observed in molecular frame C(1s) photoelectron angular distributions of methane at both low and high photoelectron energy, no interference effects are observed in the calculated β parameters, even at high photon energies. 相似文献
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Dirac R-matrix calculations of photoionization cross sections of Ni XII and atomic structure data of Ni XIII
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We performed R-matrix calculations for photoionization cross sections of the two ground state configuration 3s23p5 (2Po3/2,1/2) levels and 12 excited states of Ni XII using relativistic Dirac Atomic R-matrix Codes (DARC) across the photon energy range between the ionizations thresholds of the corresponding states and well above the thresholds of the last level of the Ni XIII target ion. Generally, a good agreement is obtained between our results and the earlier theoretical photoionization cross sections. Moreover, we have used two independent fully relativistic GRASP and FAC codes to calculate fine-structure energy levels, wavelengths, oscillator strengths, transitions rates among the lowest 48 levels belonging to the configuration (3s23p4, 3s3p5, 3p6, 3s23p33d) in Ni XIII. Additionally, radiative lifetimes of all the excited states of Ni XIII are presented. Our results of the atomic structure of Ni XIII show good agreement with other theoretical and experimental results available in the literature. A good agreement is found between our calculated lifetimes and the experimental ones. Our present results are useful for plasma diagnostic of fusion and astrophysical plasmas. 相似文献
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利用Dirac-Slater相对论平均自洽场理论,研究了不同原子体系光电离截面在不同核模型下的差异.考虑原子核大小时,核的尺寸效应使电子所感受到的有效核电荷减小,并进而影响到电子的概率分布及光电离截面等;对没有考虑原子核大小的点模型,由于不存在核的尺寸效应,出射光电子的波函数有较大相移,从而有可能出现Cooper极小.当入射光子的能量远大于相关电子的电离能时,不同核模型下电子束缚能及平均半径等的差异将相对减小,从而使光电离截面随入射光子能量的变化趋于一致. 相似文献
19.
Multiple-excitation cross sections for the scattering of 70.4 MeV 12C ions on the even neodymium isotopes are calculated by the method of angle-dependent phase shifts. The results are compared with the data. 相似文献
20.
Simon MC López-Urrutia JR Beilmann C Schwarz M Harman Z Epp SW Schmitt BL Baumann TM Behar E Bernitt S Follath R Ginzel R Keitel CH Klawitter R Kubiček K Mäckel V Mokler PH Reichardt G Schwarzkopf O Ullrich J 《Physical review letters》2010,105(18):183001
Photoionization (PI) of Fe14+ in the range from 450 to 1100 eV was measured at the BESSY II storage ring using an electron beam ion trap achieving high target-ion area densities of 10(10) cm(-2). Photoabsorption by this ion is observed in astrophysical spectra and plasmas, but until now cross sections and resonance energies could only be provided by calculations. We reach a resolving power E/ΔE of at least 6500, outstanding in the present energy range, which enables benchmarking and improving the most advanced theories for PI of ions in high charge states. 相似文献