The fourth spectrum of iridium (Ir IV)

The spectrum of three times ionized iridium, Ir IV, was investigated in the 650-2045 Å wavelength region. The analysis has led to the determination of the 5d6, 5d56s and 5d56p configurations. Twenty-nine of 34 theoretically possible 5d6 levels, 44 of 74 possible 5d56s levels and 150 of 214 possible 5d56p levels have been established. The levels are based on 1348 classified spectral lines. The level structure and transition probabilities were calculated using the orthogonal operators technique. The energy parameters have been determined by the least squares fit to the observed levels. Calculated energy values and LS-compositions obtained from the fitted parameter values are given. The level optimization procedure and the determination of uncertainties of the obtained energy level values are discussed.