We report both experimental and theoretical differential and integral excitation cross sections of atomic oxygen corresponding to the 2s 2 2p 4 3 P → 3s 3 S (130.4 nm), 2s 2 2p 4 3 P → 3d 3 D (102.7 nm), 2s 2 2p 4 3 P → 3s 3 D (98.9 nm) and 2s 2 2p 4 3 P → 3s 3 P (87.8 nm) transitions at 30, 50, and 100 eV electronimpact energies. Experimental measurements have been made in the angular range from 0 • to 25 • with a conventional electrostatic electron energy-loss spectrometer. The atomic O differential cross sections (DCSs) were put on an absolute scale by normalization to the O 2 DCS values of Johnson and Kanik (2001). Extrapolation of the measured results to larger angles was performed using theoretical calculations as a guide, and integral cross sections were derived. Theoretical calculations based on the R-matrix method, along with other available experimental data, have been compared with the current experimental results.

Electron collisional excitation strengths for transitions between the 3s23p2 and levels 3P 0,1,2 , 1D 2 , 1S 0 and from these levels to the Ðne-structure levels of the excited 3s3p3, 3s23p3d, 3s23p4s, 3s23p4p, and 3s23p4d conÐgurations of S III are calculated in R-matrix approach. We considered 49 Ðne-structure levels arising from the 27 L S 3s23p2 3P, 1D, 1S, 3s3p3 5, 3So, 1, 3Do, 1, 3Po, 3s23p3d 1, 3Po, 1,3Do, 1, 3Fo, 3s23p4s 1,3Po, 3s23p4p 1,3S, 1,3P, 1,3D, 3s23p4d 1,3Po, and 1,3Do states. These target levels are represented by fairly extensive conÐguration-interaction wave functions. The collision strengths for transitions between Ðne-structure levels are calculated by transforming the L S-coupled K-matrices to K-matrices in an intermediate coupling scheme. Complicated resonance structures converging to excited state thresholds are explicitly included in collision strengths. The e †ective collision strengths are obtained from the total collision strengths by integrating over a Maxwellian velocity distribution. These are tabulated over a wide electron temperature range (0.5È10) ] 104 K.

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The low-energy electron collision with neutral oxygen has been investigated using a modified R-matrix method based on the B-spline representation of the scattering orbitals. Integral cross sections for elastic scattering and for excitation of the 3P-1D, 3P-1S and 1D-1S transitions are presented in the energy region from threshold to 30 eV. Accurate representation of target wavefunctions has been obtained on the basis of the non-orthogonal orbitals. Both the correlation and relaxation effects are shown to be important. The close-coupling expansion consists of the 26 spectroscopic bound and autoionizing target states. A calculation with 26 spectroscopic states and 17 pseudo-states has also been carried out to check the effect of coupling to the continuum. The present results for the elastic scattering are in excellent agreement with the measurements, but large discrepancies with the existing experimental data are found for the 3P-1D and 3P-1S transitions. The excitation cross sections agree well with the recent R-matrix calculation with pseudo-states by Thomas et al (Thomas M R J, Bell K L and Berrington K A 1997 J. Phys. B: At. Mol. Opt. Phys. 30 4599) except for lower energies about 5-7 eV of threshold.

Aims. Transition probabilities and electron impact excitation collision strengths and rates for astrophysically important lines in Mg V are reported. The 86 fine-structure levels of the 2s 2 2p 4 , 2s2p 5 , 2p 6 , 2s 2 2p 3 3s, 2s 2 2p 3 3p and 2s 2 2p 3 3d configurations are included in our calculations. The effective collision strengths are presented as a function of electron temperature for solar and other astrophysical applications.Methods. The collision strengths have been calculated using the B-spline Breit-Pauli R-matrix method for all fine-structure transitions among the 86 levels. The one-body mass, Darwin and spin-orbit relativistic effects are included in the Breit-Pauli Hamiltonian in the scattering calculations. The one-body and two-body relativistic operators are included in the multiconfiguration Hartree-Fock calculations of transition probabilities. Several sets of non-orthogonal spectroscopic and correlation radial orbitals are used to obtain accurate description of Mg V 86 levels and to represent the scattering functions. Results. The calculated excitation energies are in very good agreement with experiment and represents an improvement over the previous calculations. The present collision strengths show good agreement with the previously available R-matrix and distorted-wave calculations. The oscillator strengths for E1 transitions normally compare very well with previous calculations. The thermally averaged collision strengths are obtained by integrating total resonant and non-resonant collision strengths over a Maxwellian distribution of electron energies and these are presented over the temperature range log 10 T e = 3.2−6.0 K.

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