| Abstract
| - We present new large-scale R-matrix (up to n = 4 ) scattering calculations for the electron collisional excitation of Cl-like Ni xii. We used the intermediate-coupling frame transformation method. We compare predicted and observed line intensities using laboratory and solar spectra, finding good agreement for all the main soft X-ray lines. With the exception of the three strongest transitions, large discrepancies with previous estimates are found, especially for the decays from the lowest 3s 2 3p 4 3d levels. This includes the forbidden UV lines. The atomic data for the n = 4 levels are the first to be calculated. We revise previous experimental energies, and suggest several new identifications. We point out the uncertainty in the wavelength of the 3s 2 3p 52P 1/2-3s 2 3p 4 3d 2D 3/2 transition, which is important for density diagnostics.
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