Table notes: Energy levels marked with an asterisk indicate levels with experimental values taken from Clear et al. 2022 and Clear et al. 2023, rounded to two decimal places; all other levels correspond to calculated eigenvalues. Energy level labels given in this table denote the largest eigenvector component only and are provided for guidance. Definitive energy level assignments for experimentally determined levels were established following a detailed term analysis and are reported in Clear et al. 2022 and Clear et al. 2023. For transitions involving a calculated eigenvalue, wavelengths and wavenumbers should not be considered spectroscopically accurate. For transitions between purely experimental energy levels, denoted with an asterisk, the reader is referred to Clear et al. 2022 and Clear et al. 2023 for Ritz wavelengths and associated uncertainties. Wavelengths between 200 nm and 2 µm are given as air wavelengths and as vacuum wavelengths outside this region. Uncertainties in log(gf) values and A-values are estimated to be 20% for strong lines with S > 2 and 40% for lines with 0.02 < S < 2; uncertainties are not provided for weaker transitions.

This dataset corresponds to Table A2 in the paper “Calculated oscillator strengths and transition probabilities of singly ionised nickel (Ni II)” by C. P. Clear et al., published in Astronomy & Astrophysics (2026). It contains the calculated transition probabilities (A-values) and oscillator strengths (log(gf)) for electric dipole (E1) transitions of singly ionised nickel (Ni II). These values were obtained using the orthogonal operator method, as detailed in the publication. The table includes transitions between observed and predicted energy levels, providing essential atomic data for astrophysical and laboratory plasma modelling.