Electron impact excitation of C IV

Energy levels and radiative rates for transitions among the lowest 24 fine-structure levels belonging to the ls(2) nl (n <5) configurations of Li-like C IV have been calculated using the fully relativistic GRASP code. Additionally, collision strengths for transitions among these levels have been computed over a wide energy range below 28 Ry, using the Dirac Atomic R- matrix Code. Resonances have been resolved in a fine energy mesh in order to calculate the effective collision strengths. Results for radiative rates, collision strengths, and effective collision strengths are presented for all transitions. Comparisons with other available results are made, and the accuracy of the present data is assessed. Energy levels are expected to be accurate to within 1%, while other parameters are probably accurate to better than 20%.

Electron impact excitation of Fe XIII

Energy levels and radiative rates for transitions among the lowest 97 fine-structure levels belonging to the (1s(2) 2s(2) 2p(6)) 3 s(2) 3p(2), 3s3p(3), 3s(2) 3p3d, 3p(4), 3s3p(2) 3d and 3s(2) 3d(2) configurations of Fe XIII have been calculated using the fully relativistic GRASP code. Additionally, collision strengths for transitions among these levels have been computed using the Dirac Atomic R-matrix Code (DARC) of Norrington & Grant (2004). Radiative rates and oscillator strengths are tabulated for all allowed transitions among the 97 fine-structure levels, while collision strengths are reported for some transitions at a few energies above thresholds. Comparisons are made with the available results, and the accuracy of the data is assessed.

Electron impact excitation of Mo XXXIV

Energy levels and radiative rates for transitions among the lowest 60 fine-structure levels belonging to the (1s(2)) 2s(2)2p(5), 2s2p(6), and 2s(2)2p(4)3l configurations of F-like Mo XXXIV have been calculated using the fully relativistic GRASP code. Additionally, collision strengths for transitions among these levels have also been computed over a wide energy range below 3200 Ry. using the Dirac Atomic R-matrix Code. Resonances have been resolved in a fine energy mesh in order to calculate the effective collision strengths. Results for radiative rates, collision strengths, and excitation rates are presented for transitions from the lowest three levels to higher lying states. Comparisons with other available results are made, and the accuracy of the present data is assessed. Energy levels are expected to be accurate to within 1%, while other parameters are probably accurate to better than 20%.

Electron impact excitation of carbon-like calcium

Collision strengths for transitions among the energetically lowest 46 fine-structure levels belonging to the (1s(2)) 2s(2)2p(2), 2s2p(3). 2p(4), 2s(2)2p3s, 2s(2)2p3p and 2s(2)2p3d configurations of Ca XV are computed. over an electron energy range of 50 less than or equal to E less than or equal to 300 Ryd. using the recent Dirac Atomic R-matrix Code (DARC) of Norrington and Grant. All partial waves with J less than or equal to 40.5 have been included, and the contribution of higher partial waves has been added to ensure the convergence of collision strengths for all transitions and at all energies. The results are compared with those available in the literature, and the accuracy of the data is assessed.

Improved data for solar flare X-ray spectral analysis

The inclusion of collisional rates for He-like Fe and Ca ions is discussed with reference to the analysis of solar flare Fe XXV and Ca XIX line emission, particularly from the Yohkoh Bragg Crystal Spectrometer (BCS). The new data are a slight improvement on calculations presently used in the BCS analysis software in that the discrepancy in the Fe XXV y and z line intensities (observed larger than predicted) is reduced. Values of electron temperature from satellite-to-resonance line ratios are slightly reduced (by up to 1 MK) for a given observed ratio. The new atomic data will be incorporated in the Yohkoh BCS databases. The data should also be of interest for the analysis of high-resolution, non-solar spectra expected from the Constellation-X and Astro-E space missions. A comparison is made of a tokamak S XV spectrum with a synthetic spectrum using atomic data in the existing software and the agreement is found to be good, so validating these data for particularly high-n satellite wavelengths close to the S XV resonance line. An error in a data file used for analyzing BCS Fe XXVI spectra is corrected, so permitting analysis of these spectra.

Effective collision strengths for electron impact excitation of C1III

Effective collision strengths for electron-impact excitation of the phosphorus-like ion Cl III are presented for all fine- structure transitions among the levels arising from the lowest 23 LS states. The collisional cross sections are computed in the multichannel close-coupling R-matrix approximation, where sophisticated configuration-interaction wave functions are used to represent the target states. The 23 LS states are formed from the basis configurations 3s(2)3p(3). 3s3p(4). 3s(2)3p(2)3d, and 3s(2)3p(2)4s, and correspond to 49 fine- structure levels, leading to a total possible 1176 fine- structure transitions. The effective collision strengths. obtained by averaging the electron collision strengths over a Maxwellian distribution of electron velocities. are tabulated in this paper for all 1176 transitions and for electron temperatures in the ranges T(K) = 7500-25.000 and log T(K) = 4.4-5.3. The former range encompasses the temperatures of particular importance for application to gaseous nebulae. while the latter range is more applicable to the study of solar and laboratory-type plasmas. (C) 2001 Academic Press.

Effective collision strengths for electron impact excitation of Si VIII

Effective collision strengths for electron-impact excitation of the nitrogen-like ion Si VIII are presented over the wide range of electron temperatures log T(K) = 4.0-6.5. All 231 fine- structure transitions among the 22 fine-structure levels arising from the lowest 11 LS target states (2s(2)2p(3), 2s2p(4), 2p(5), and 2s(2)2p(2)3s) are considered in the tabulation. The collision strengths are evaluated in a multi- channel R-matrix approach, and the corresponding effective collision strengths are obtained by averaging these over a Maxwellian distribution of electron velocities. Comparisons are made with recent distorted-wave results at high incident electron energies. Differences of up to 20% are found, particularly for some allowed transitions. (C) 2003 Elsevier Inc. All rights reserved.

Experimental observation of dissociative electron attachment to S2O and S2O2 with a new spectrometer for unstable molecules

A new spectrometer, electron radical interaction chamber, has been developed to study dissociative electron attachment to unstable molecules such as free radicals. It includes a trochoidal electron monochromator and a time-of-flight mass spectrometer. Radicals are generated with a microwave discharge at 2.45 GHz. Preliminary data are presented for radicals formed when a mixture of helium and sulphur dioxide was passed through the microwave discharge. Several new resonances are observed with the discharge on. Resonances at 0 eV (S-), 0.8, 1.2, 3.0 eV (SO-) and 3.7 eV (SO- and S2O-) are assigned to the radical S2O2 and a resonance at 1.6 eV (S-) is assigned to S2O. No new resonances have been assigned to SO, which was also generated in the microwave discharge.

Giant resonances in cold electron scattering by CS2

Experimental data are presented for the scattering of cold electrons by CS2, for both integral and backward scattering, between a few meV and a few hundred meV impact energy. Giant resonances with cross sections in excess of 50 Angstrom(2) are observed below 100 meV, associated with the transient formation of CS2- at 15 meV and with the bend and symmetric stretch of CS2 at thresholds of 49 and 82 meV, respectively. The resonance at 49 meV is 2 orders of magnitude greater in cross section than a dipole impulsive model predicts. These structures are superimposed on a sharp rise in the scattering cross section at low energy, which may be attributed to virtual state scattering.

Pair production and electron capture in relativistic heavy-ion collisions

Results are presented for simulations of electron-positron pair production in relativistic heavy-ion collisions leading to electron capture and positron ejection. We apply a two-center relativistic continuum distorted-wave model to represent the electron or positron dynamics during the collision process. The results are compared with experimental cross-section data for La57+ and Au79+ impact on gold, silver, and copper targets. The theory is in good agreement with experiment for La57+ impact, verifying the result that the process increases in importance with both collision energy and target atomic number, and improves upon previous simulations of this process.

State-selective one-electron capture by slow state-prepared N2+(P-2) ground-state ions in collisions with hydrogen atoms

The technique of double translational energy spectroscopy.(DTES), recently successfully developed in this laboratory for use with targets of atomic hydrogen, has been used to study one-electron capture by ground-state N2+(2s22p)(2)p(0) ions in collisions with hydrogen atoms at energies within the range 0.8-6.0 keV. Cross sections for the formation of the main excited product channels have been determined. The measurements allow a re-evaluation of our previous TES measurements carried out with N2+ primary beams containing an admixture of metastable N2+(2s2p2)(4)p ions. The main findings of these earlier measurements are confirmed and the DTES measurements now remove any ambiguity in interpretation of the experimental data. While recent theoretical studies correctly predict the two main N+ D-3(0) and P-3(0) product channels, the quantitative agreement with experiment is only partially satisfactory.

Measurement of highly transient electrical charging following high-intensity laser-solid interaction

The multi-million-electron-volt proton beams accelerated during high-intensity laser-solid interactions have been used as a particle probe to investigate the electric charging of microscopic targets laser-irradiated at intensity similar to10(19) W cm(2). The charge-up, detected via the proton deflection with high temporal and spatial resolution, is due to the escape of energetic electrons generated during the interaction. The analysis of the data is supported by three- dimensional tracing of the proton trajectories. (C) 2003 American Institute of Physics.

Electron collisions with iron peak elements: a computational grand challenge

This paper discusses the calculation of electron impact collision strengths and effective collision strengths for iron peak elements of importance in the analysis of many astronomical and laboratory spectra. It commences with a brief overview of R-matrix theory which is the basis of computer programs which have been widely used to calculate the relevant atomic data used in this analysis. A summary is then given of calculations carried out over the last 20 y for electron collisions with Fe II. The grand challenge, represented by the calculation of accurate collision strengths and effective collision strengths for this ion, is then discussed. A new parallel R-matrix program PRMAT, which is being developed to meet this challenge, is then described and results of recent calculations, using this program to determine optically forbidden transitions in e- – Ni IV on a Cray T3E-1200 parallel supercomputer, are presented. The implications of this e- – Ni IV calculation for the determination of accurate data from an isoelectronic e- – Fe II calculation are discussed and finally some future directions of research are reviewed.

Electron-ion scattering

Recent advances in the elucidation of electron-ion scattering phenomena is reviewed, with particular emphasis on the new generation of experiments where scattered electrons are analysed and detected, The sensitivity of measurements as a probe of collision dynamics, application to plasma studies, and future directions are considered.

Electron and laser interactions with positive ions

Recent progress in laboratory-based electron-ion scattering is reviewed, and the sensitivity of observed interference structure as a probe of collision dynamics is discussed. The extension of our use of positive ions as scattering targets to photon-ion interactions is demonstrated with the first ion-beam measurements for the fragmentation of a molecular ion, H-2(+), using intense femtosecond laser pulses.