Isoelectronic study of triply excited Li-like states (original) (raw)
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Fully differential cross sections for Li2+-impact ionization of Li(2s) and Li(2p)
Journal of Physics B: Atomic, Molecular and Optical Physics
A semiclassical impact parameter version of the continuum distorted wave-Eikonal initial state theory is developed to study the differential ionization of Li atoms in collisions with Li 2+ ions. Both post and prior forms of the transition amplitude are considered. The fully differential cross sections are calculated for the lithium targets in their ground and their first excited states and for the projectile ions at 16 MeV impact energy. The role of the internuclear interaction as well as the significance of the post-prior discrepancy in the ejected electron spectra are investigated. The obtained results for ejection of the electron into the azimuthal plane are compared with the recent measurements and with their corresponding values obtained using a fully quantum mechanical version of the theory. In most of the cases, the consistency of the present approach with the experimental and the quantum theoretical data is reasonable. However, for 2p-state ionization, in the cases where no experimental data exist, there is a considerable difference between the two theoretical approaches. This difference is questionable and further experiments are needed to judge which theory makes a more accurate description of the collision dynamics.
Japan Atomic Energy Research Institute Report JAERI-Data/Code, 1994
Analytic expressions fitted to Barnett's recommended data are given for the cross sections of excitation and spectral line emission by H, H+, He+, He, and He2+ colliding with atoms and molecules. The expressions use the semiempirical functional forms proposed by Green and McNeal and some modified forms to make it possible not only to interpolate but also to extrapolate the recommended data.
The effects of coupling to the target continuum on the electron-impact excitation of Li
Journal of Physics B: Atomic, Molecular and Optical Physics, 2003
We have investigated the effects of coupling to the continuum and high bound states on the electron-impact excitation of He-like Li + using the R matrix with pseudostates (RMPS) method. Previous studies on this ion have focused on transitions from the ground state to the n = 2 terms. In this work, we have determined collision strengths between all 19 terms through n = 4. We present the results of two RMPS calculations with different numbers of pseudostates in order to study the convergence of the collision strengths with the size of the pseudostate expansion. In addition, we compare the RMPS collision strengths with the results of an R-matrix calculation without pseudostates in order to determine the influence of the continuum coupling as a function of electron energy. As one might expect, coupling to the target continuum has quite large effects on the collision strengths for excitation to the n = 3 and 4 terms at energies above the ionization limit. However, we find that these effects are also significant for excitation to the n = 2 terms and that they persist down to energies just above the excitation thresholds. The experience gained from this work will allow us to pursue similar studies in more complex target systems. Furthermore, the results of our largest RMPS calculation provide the most complete and accurate set of excitation data for this ion, which is of significant importance to research in controlled nuclear fusion.
Physical Review Letters, 2000
We have measured the angle-resolved energy dependence of the electrons emitted over the energy range of the triply excited 2s 2 2p 2 P lithium resonance using synchrotron radiation. We have also calculated the behavior of the angular distribution parameter b using the R-matrix approximation. Experimental and theoretical results are in good agreement and show deep minima in the 1s2p 1, 3 P ionic channels. The energy at which the minima occur does not coincide with the resonance energy, but is shifted towards higher energy. PACS numbers: 32.80.Hd, 32.80.Fb In this Letter, we present the results of a new experiment investigating the angular distribution of electrons emitted in autoionization of the lowest-energy triply excited state of atomic lithium. We made a critical comparison of the data with the results of advanced Rmatrix calculations performed in order to interpret the energy behavior of the angular distribution parameter b. Photons from the Advanced Light Source (ALS) photoexcited the 2s 2 2p 2 P hollow lithium state both on and off resonance. The electrons emitted were angularly analyzed with a cylindrical mirror analyzer (CMA) electron spectrometer. The experimental results reveal a pronounced energy dependence of the angular distribution parameter b in the Li 1 1s2p 1, 3 P´l satellite channels, in good agreement with theoretical prediction. Both experiment and theory show that the minima in the b profiles occur on the high energy side of the resonance.
Electron-impact-excitation cross sections of lithiumlike ions
Physical Review A, 1997
We present an easy to use expression for cross sections of electron-impact-induced 1s 2 nl→1s 2 nЈlЈ excitation transitions with 2рnрnЈр4 in multiply charged ions of lithium isoelectronic sequence. This expression is based on our computations by convergent close-coupling ͑CCC͒ and Coulomb-Born with exchange and normalization ͑CBE͒ methods. We show scaling of the CCC and CBE cross sections with atomic number Z and use this scaling for presentation of the cross-section data. For 6рZр30 the scaling is accurate to better than Ϯ20% at any energy except in the vicinity of resonances. Contributions from indirect excitation channels do not scale with Z; however, for calculation of excitation rates it is enough to average locally these contributions over energy and to take them into account in a frame of a general scaling-based expression for the cross sections. For excitation rates, total inaccuracy caused by all simplifications in the cross-section presentation is likely to be less than Ϯ30% even for most risky cases. This assessment is based on comparison of excitation rates, computed using our scaling-based expression for the cross sections, with the excitation rates, computed using high-resolution ͑CCC and R matrix͒ cross sections and experimental data.
Charge-Changing Processes in Collisions between Li-like Ions and He2+
Physica Scripta, 2001
By means of a crossed-beams technique the total cross sections for charge transfer and ionization in He 2 B 2 collisions have been measured at barycentric energies from 10 to 256 keV and from 40 to 240 keV, respectively. Moreover, the angular-di¡erential cross sections for charge transfer at CM energies of 10.18 and 15.3 keV have been determined. The total and di¡erential cross sections are calculated with the Basis Generator Method (BGM) and are in good agreement with the experimental data.
Transfer and excitation processes studied in H-like S and Li-like and H-like F colliding with H2
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1989
We have studied transfer and simultaneous excitation by three different experimental techniques. Coincidences between two K X rays were measured for S 15+ , coincidences between one K X ray and the charge exchanged projectile for Li-like F and projectile Auger electrons for H-like F in each case colliding with H2. For all three collision systems, the measured cross sections are dominated by Resonant Transfer and Excitation (RTE). Also, for the F projectiles, strong contributions from Two Electron Transfer and Excitation (2eTE) were found.
Signature of triply excited Li-like V states in ion–solid collisions
Physics Letters A, 2016
The transitions originating from triply excited, doubly autoionizing states of Li-like V formed in beam-foil experiments detected within a set of blended spectroscopic profiles have been assigned tentatively by the Hartree-Fock calculations including relativistic corrections and multi-configuration interactions as perturbations. The x-ray decay channels from the triply excited states such as 3p 3 4 S, 2p 2 np 4 S (n ∼ 12) through radiative transitions to the ground state via two or more steps have been observed.
High-Resolution Measurements of Electron-Impact Ionization Cross Sections for LI-Like Ions
Le Journal de Physique Colloques, 1989
Pour une expCrience avec des faisceaux croisCs des Clectrons et des ions une technique experimentale a CtC divelopp6e qui permet de mesurer des sections efficaces pour l'ionisation des ions par impact Blectronique avec une impr6cision moins de 0.1 %. A ce degrg de grBcision il est possible de r6aliser une spectroscopie des Ctats excitCs intermediaires des ions qui contribuent B l'ionisation nette vers le Drocessus de l'autoionisation simale et multi~le.