Spectroscopic study of odd-parity excited levels of atomic gadolinium in the 28700–31500 cm⁻¹ region using a three-color three-step resonance ionization pathway

The three-color, three-step resonance ionization spectroscopy technique was employed to investigate the odd-parity excited states of gadolinium in the 28700–31500 cm⁻¹ energy region. Spectra scanned without λ₁ led to the identification of 101 interference peaks, which were excluded from subsequent studies. A total of 40 odd-parity excited states were observed from scans of nine even-parity lower levels, including 19 states reported here for the first time. Unique J values were assigned to 39 levels using the electric dipole selection rule. Comparison with previous studies confirms the reliability of the present results, with the absolute energy accuracy estimated to be better than ±0.1 cm⁻¹.