Calculations Of Collision Strengths Research Articles

Electron impact excitation of Fe2+. I. A 17-level fine-structure calculation

A Breit-Pauli R-matrix calculation for the electron impact collision strengths of Fe2+ is reported involving transitions among the lowest 17 levels corresponding to the 3d6 5D, 3H, 3P, 3F and 3G terms. Resonance structures are elucidated for the first time. The calculated collision strengths at impact energies above the resonance region show some disagreements with those from an earlier five-term R-matrix calculation of Garstang et al. (1978) for example the 5D-3H and 3H-3P collision strengths are a factor of three larger than in the earlier calculation. The present calculation also investigates the variation of collision strengths with energy; in particular, resonances are found to enhance the thermally averaged effective collision strengths by up to 40% for transitions among the fine-structure levels of the 5D ground state. Effective collision strengths for all transitions among the 17 levels are tabulated for electron temperatures 10000 K and 20000 K.

Electron scattering by Se XXV (neon-like selenium) using the Dirac R-matrix method

The Dirac R-matrix method has been used to calculate collision strengths for the scattering of electrons with kinetic energy 100-300 Ryd by a neon-like selenium (Se24+) target. In these calculations the 27 jj-coupled levels arising from the configurations 1s22s22p6, 1s22s22p53s, 1s22s22p53p and 1s22s220p53d are included. Collision strengths converged to within 5% are obtained with twenty-four (N+1)-particle collision symmetries (partial waves). The rates for radiative transitions between the 27 levels have also been calculated. The authors' results are compared with previous calculations.

Electron impact excitation of the 3s23p4 levels of Ar III

The authors have calculated collision strengths for electron excitation of the 3s23p4 3Pe0.1,2, 1De2 and 1Se0 levels of Ar III using the R-matrix method. They included the five states 3s23p4 3Pe, 1De, 1Se and 3s3p53P0, 1P0, which they represented by configuration interaction wavefunctions. These wavefunctions yield oscillator strengths for allowed transitions between the levels which are in good agreement with the experimental values. Reactance matrices were obtained in LS coupling and were transformed using JAJOM to give the fine-structure collision strengths. The latter have been averaged over a Maxwellian electron velocity distribution to give the effective collision strengths, for temperatures from 4000 to 24000 K. The calculated electron excitation rates are up to 50% larger than previous values at 10000 K due to resonance structure in the collision strengths.

Effective collision strengths among fine-structure levels of CA XV

view Abstract Citations (12) References (31) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Effective Collision Strengths among Fine-Structure Levels of CA XV Aggarwal, K. M. ; Berrington, K. A. ; Keenan, F. P. Abstract The R-matrix program is used to calculate collision strengths Omega for 190 fine-structure transitions among the 1s2 2s2 2p2, 1s2 2s 2p3, and 1s2 2p4 configurations of Ca XV in the energy range of 0-100 Ry. Relativistic effects are included in the computations of Omega through term coupling coefficients. The effective collision strengths Tau, obtained by averaging Omega over a Maxwellian distribution of electron velocities, are listed for all transitions in the temperature range of 10 to the 6th to 10 to the 7th K. The effects on the calculated Omega and Tau values of term coupling and configuration-interaction in the target are examined, and the importance of including relativistic effects is noted, particularly for spin and parity changing transitions at the higher energies and temperatures. Publication: The Astrophysical Journal Supplement Series Pub Date: April 1990 DOI: 10.1086/191435 Bibcode: 1990ApJS...72..815A Keywords: Atomic Energy Levels; Atomic Physics; Calcium; Electron Scattering; Fine Structure; Electron Energy; Electron Transitions; Ground State; Relativistic Effects; Solar Flares; Wave Functions; Atomic and Molecular Physics; ATOMIC PROCESSES; TRANSITION RATES full text sources ADS | Related Materials (1) Erratum: 1991ApJS...77..441A

Collision strengths for dipole-allowed transitions in S II

Calculations of collision strengths for electron-impact excitations of S II from the ground state 3p3 4S0 to excited states 3p4 4P, 3d 4F, 3d 4D, 4s 4P, and 3d 4P were carried out using the R-matrix code described by Berrington et al. (1978) and the NIEM code described by Henry et al. (1981). Results are presented for the thermally averaged collision strengths for the five-state and six-state calculations. Convergence behaviors were examined by comparison with the six-state calculations and the previously obtained two-state calculations. Uncertainties for these transitions were estimated to be within 20 percent, except for the 4S0 - 3p4 4P transition in which a 40 percent uncertainty was estimated.

Fully relativistic and quasirelativistic distorted-wave methods for calculating collision strengths for highly charged ions.

A rapid fully relativistic distorted-wave method for calculating collision strengths for highly charged ions is described. A more rapid quasirelativistic approximation in which the average over j value -1 is used for the relativistic quantum number \ensuremath{\kappa} for the free electrons is also discussed. Very rapid, but accurate, procedures for obtaining results for a given class of transitions for a large portion of an isoelectronic sequence by using fits to Z after making detailed calculations for only a few values of Z are described. Results by the present methods are compared with more elaborate relativistic distorted-wave calculations by other workers, principally for neonlike and nickel-like ions, but also comparisons for He-like, Li-like, and Na-like ions are discussed. In addition, comparisons with a few experimental results for neonlike barium could be made. Generally very good agreement is obtained with all these data.

Electron excitation of the 1s22s22p52Po3/2-2Po1/2transition and analysis of the 1s22s2p6nl resonances for Ne II and Mg IV

The author has calculated collision strengths for electron excitation of the 1s22s22p5 2Po3/2-2Po1/2 transition in Ne II and Mg IV using the R-matrix method. The author has included the 1s22s22p5 2Po and 1s22s2p6 2Se states, which were represented by sophisticated configuration interaction wavefunctions. Reactance matrices were obtained in LS coupling and transformed using JAJOM to give the fine-structure collision strengths. These have been averaged over a Maxwellian electron velocity distribution to give the effective collision strengths, which we have fitted as analytic functions of temperature between 0 and 40000 K. To estimate the accuracy of the results the author has calculated the positions and widths for the lower members of the 1s22s2p6ns and 1s22s2p6np resonance series. The results are in good agreement with experiment and with previous theory for both Ne II and Mg IV.

A comparison of the C III, O V, F VI, and NE VII Delta N = 0 (2-2) line emissions from a laboratory plasma with theoretical predictions and astrophysical observations

Spectra of the Delta n = 0 (2-2) transitions of Be I-like ions, C III, O V, F VI, and Ne VII emitted from the TEXT tokamak, were measured with photometrically calibrated instrumentation and compared to the predictions of several models which differ in their treatment of electron impact excitation, using either the distorted wave or R-matrix approach. It was found that the ions from C III to Ne VII were located near the edge of the plasma, at densities between 10 to the 12th and 13th/cu cm. The experimental line ratios were compared with several sets of computations. Agreement is obtained between the experimental data and computations by using the R-matrix technique. This leads to the conclusion that the effect resonances must be included in collision strength calculations, particularly at low nuclear charge. The results show that the line ratios studied may be used with confidence as electron density diagnostics for laboratory or astrophysical plasmas.

Improved excitation rate coefficients for the N = 2 and N = 3 levels of CA XIX and Fe XXV including fine structure

Reently calculated collision strengths, including relativistic and resonance effects, are employed to compute Maxwellian averaged collision strengths for 78 transitions involving states of principal quantum numbers 2-1 and 3-1 in Ca XIX and Fe XXV. These rate parameters are tabulated at temperatures of interest in astrophysical and labortory plasmas with radiation in the hard X-ray wavelength range. For some transitions, significant differences are found with the earlier calculations of Pradhan, Norcross, and Hummer (1981).

Dielectric recombination. II. Effects on cross sections for inelastic collisions between electrons and atomic ions

For pt.I see ibid., vol.18, p.1589 (1985). Formulae obtained by Bell and Seaton in the first paper of the present series are used to calculate collision strengths for the 1 1S-21S transitions in O6+ at energies below the 21P threshold. Radiative decays lead to modifications of autoionising resonance profiles and substantial reductions in collision strengths averaged over resonances.

Discrepancy between electron heating and cooling rates derived from atmosphere Explorer-C measurements

The present theory of electron temperature in the daytime mid-latitude ionosphere is tested by using Atmosphere Explorer-C measurements. In the region below 300 km, where a balance is expected between electron heating by photoelectron impact and electron cooling to ions and neutrals, we find an imbalance in which the cooling rate is consistently higher than the heating rate. The shapes of the altitude profiles also differ substantially. The cooling rate has a sharp peak at about 220 km, while the heating rate exhibits a broad peak about 30 km lower. Improved agreement is achieved at higher altitudes by using an oxygen fine structure loss rate smaller by a factor of 2, based on more recent collision strength calculations. Although this improves the overall agreement of the heating and cooling rates, the shape discrepancy remains, and the new cooling rate falls consistently below the heating rate below 200 km.

Low-energy scattering of electrons by atomic oxygen

The method of polarized pseudostates has been used to calculate cross sections for the elastic scattering of electrons by atomic oxygen. These pseudostates are added to the close-coupling expansion to give a polarization potential in agreement with experimental values of polarizability. The resulting elastic cross sections are in good agreement with other theoretical calculations as well as with experiment for energies up to 10 eV. The reactance matrices obtained in this calculation have been used to calculate collision strengths for fine-structure transitions in the ground-state $^{3}P$ term for electron temperatures above 5000\ifmmode^\circ\else\textdegree\fi{} K.

Calculated collision strengths for electron impact excitation of NV

Five-state close-coupling calculations have been carried out to obtain collision strengths for electron excitation of Nv. The results are compared with those obtained from other approximations and the validity of these approximations is discussed.

On the validity of the distorted wave method in electron-atom collision theory

The comparison of distorted wave and close coupling calculations of collision strengths for transitions in C III excited by electron collisions indicates that the distorted wave method is sufficiently accurate for many astrophysical and laboratory applications even for atoms which are only twice ionized.

On the Forbidden Emission Lines of Iron in Seyfert Galaxies

view Abstract Citations (116) References (26) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS On the Forbidden Emission Lines of Iron in Seyfert Galaxies Nussbaumer, H. ; Osterbrock, D. E. Abstract The excitation of the [Fe vr ], [Fe x], and [FE xivj emission lines in Seyfert galaxies is discussed, with special reference to the interpretation of the strengths of these lines in NGC 4151. The [Fe vIr] lines probably arise in the same regions as the [Ne vi lines. Newly calculated collision strengths for [Fe v j are presented, and they are used to find the relative Fe abundance in NGC 4151, approximately N(Fe)/ N(H) = 1.4 X 10- , with an uncertainty of approximately a factor of 2. The [Fe xi and [Fe xivi lines may arise in a high-temperature gas, as Oke and Sargent suggested. On this model the amount of hightemperature gas is calculated by using published collision strengths for [Fe xlvi and published plus estimated collision strengths for [Fe xi. The radiation from this high-temperature gas, if it exists, is energetically sufficient to photoionize much of the "cool" gas in which the other observed emission lines are emitted. Thus the hot gas may be the primary source of photoionization. It may be heated by collisions between clouds moving with velocities corresponding to the observed line widths. Publication: The Astrophysical Journal Pub Date: September 1970 DOI: 10.1086/150585 Bibcode: 1970ApJ...161..811N full text sources ADS | data products NED (1)

Excitation of C III] λ 1909 and Other Semiforbidden Emission Lines in QSOs and Nebulae

view Abstract Citations (52) References (14) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Excitation of C III] λ 1909 and Other Semiforbidden Emission Lines in QSOs and Nebulae Osterbrock, D. E. Abstract Newly calculated collision strengths for 2s2 of C+2 and other isoelectronic ions are integrated over a Maxwellian distribution to give effective collision strengths. The fraction of excitations leading to emission of a line photon is calculated in various density ranges. The possibility of determinin electron densities in the range cm-i from the relative strengths of the two components ? is pointed out. Publication: The Astrophysical Journal Pub Date: April 1970 DOI: 10.1086/150401 Bibcode: 1970ApJ...160...25O full text sources ADS |

Collision Strengths for Excitation of Forbidden Lines

New calculations of collision strengths are being made for ions in configurations npq, n = 2 and 3 and q = 1–5. Wave functions for the entire system are represented by sums over anti-symmetrized products of ion functions and orbitals for the colliding electron, and sets of coupled integro-differential equations are obtained for the colliding electron radial functions. The main approximation is neglect of coupling to configurations other than npq. Calculations are made using improved forms of the exact resonance and distorted wave approximations. For the 2pq ions it is found that the dominant contributions come from the p-waves; the exact resonance approximation is used for the p-waves and the distorted wave approximation is used for all other partial waves. It is considered that the results obtained should approximate closely to those which would be obtained from full solutions of the coupled equations. For the 3pq ions the dominant contributions come from the p-waves; for these ions the distorted wave approximation is used for all partial waves.