Study of even-parity autoionization resonances of atomic uranium by three-color optogalvanic spectroscopy

We report our investigation on the even-parity autoionization (Al) resonances of atomic uranium in the energy region 52,850-53,350 cm-1, using the three-color optogalvanic spectroscopy technique in a U-Ne hollow cathode discharge lamp with three pulsed dye lasers. To the best of our knowledge, this is the first report of observation of even-parity Al states in atomic uranium lying more than 2000 cm-1 above the ionization limit. We have used four different excitation schemes, starting from the lowest metastable state of uranium at 620 cm-1 (K055). We have identified 102 new even-parity Al resonances in atomic uranium and assigned probable total angular momentum (J) values to these resonances. By observing 25 out of these 102 Al resonances through more than one excitation pathway, the ambiguity in the assignment of their J values has been reduced considerably.