Odd-parity autoionizing levels of uranium observed by two-color two-step photoionization optogalvanic spectroscopy

Two-color two-step photoionization optogalvanic spectroscopy was performed using high-repetition-rate titanium sapphire lasers and a uranium hollow cathode lamp to find the two-step resonance ionization schemes of uranium. Many ionization transitions were observed by exciting uranium atoms in a ground state into five, even parity, excited levels with the first-step laser and by scanning the second-step laser wavelengths. By blocking the first-step laser, single-color, two-photon ionization transitions were also identified. From these results, we have found more than 50 odd-parity autoionizing levels of uranium in the energy, ranging from the ionization potential (49958.4 cm⁻¹) to 51 150 cm⁻¹. The determined energy levels are within ∼±1 cm⁻¹ of previously reported values. (paper)