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

Abstract

We report our investigation on the even-parity autoionization (AI) 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 AI 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 ( 5 K 0 5 ). We have identified 102 new even-parity AI resonances in atomic uranium and assigned probable total angular momentum (J) values to these resonances. By observing 25 out of these 102 AI resonances through more than one excitation pathway, the ambiguity in the assignment of their J values has been reduced considerably.

High-Resolution Spectroscopy

“…This technique has been employed by large number of groups [1] worldwide for various types of spectroscopic investigations. Our group has also used it extensively both in singlecolor and multicolor excitation spectroscopy [2,3]. We have also developed what is called photoionization optogalvanic spectroscopy.…”

“…This has the consequence that higher energy regions can be explored. This was made use of in our experiments by starting from 620 cm 1 metastable level by using Rh 6G-based dye lasers and employing a three-step optogalvanic spectroscopy to explore autoionization states in the energy region 52,850-53,350 cm 1 -a totally unchartered territory so far [3]. This way, by using four different excitation schemes, as given in [3], we identified 102 new even-parity autoionisation states and assigned them probable J values.…”

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

“…Considering the wavelength range of the second harmonic of the Ti:Sa laser, the even-parity levels (around 25 000 cm −1 ) and the odd-parity autoionization levels around the ionization potential (IP) of uranium (49958.4 cm −1 [16]) are suitable for a two-step resonant ionization. So far, RIMS [17][18][19][20][21][22][23][24][25] and PIOGS [9,[26][27][28] report some autoionizing levels of uranium. However, most of them are even-parity levels suited for a three-step ionization scheme.…”