Semi-empirical analysis of oscillator strengths for Nb II

•The semi-empirical method of parameterization of oscillator strengths.•Illustration of the method application for the example of Nb II data.•Predicted values of oscillator strengths for transitions from odd levels of Nb II in a wide spectral range.

Semi-empirical wave functions, proven via comparison of the expected and experimental hyperfine structure constants and gJ-factors in previous papers, were used for the parametrization of the oscillator strengths for electric-dipole transitions in Nb II, where reliable experimental data were available. The angular coefficients of the transition matrix in pure SL coupling were found from straightforward Racah algebra. The transition matrix was transformed into the actual intermediate coupling by the fine structure wave functions. The transition integrals were treated as free parameters in the least squares fit to experimental gf values. This procedure allowed us to obtain the values of transition integrals and predict the values of oscillator strengths for transitions from odd levels in a wide spectral range.