Total angular momenta of even-parity autoionizing levels and odd-parity high-lying levels of atomic uranium

Abstract

Using three-step resonance ionization spectroscopy, over 200 even-parity autoionizing (AI) levels of atomic uranium, including Rydberg series converging to the second lowest ionic level (6L 11/2o), were observed in the 49 930–51 200 cm−1 energy range. Total angular momenta (J values) of these levels were determined by a polarization combination method as well as a method based on the J-momentum selection rule. Using the AI levels of which J values were determined unambiguously, unique J values were also assigned for about 70 high-lying odd-parity levels. The observed J-dependence on autoionization linewidth is interpreted as being due to a centrifugal potential barrier.

High-resolution triple-resonance autoionization of uranium isotopes

“…Following earlier observations [25,26], this is attributed to a centrifugal barrier effect between the high J of the AI state and the lower J of the resulting ionic core. In the current case, energetics of just above threshold ionization require that the resulting ion be in the J = 9 / 2 ground state.…”

“…J 2 are the spectra (Fig. 3) in which the AI levels are observed; J AI are our assignments compared to literature values from [25].…”

“…There have been many investigations on uranium using broad-band pulsed dye lasers, which is favorable for AVLIS where high efficiency and only moderate isotopic selectivity are needed. The importance of autoionizing (AI) levels for enhancing photoionization efficiency was recognized early [6], and recent studies found a large number of AI levels with high ionization cross-sections, including intense Rydberg series, within the first 300 cm À 1 above the first ionization potential [25]. However, these experiments used pulsed lasers with linewidths !…”

In-source resonance ionization spectroscopy of high lying energy levels in atomic uranium

“…In the spectrum of uranium the occurrence of a large number of auto-ionizing resonances is expected due to the existence of four optical active electrons in open shells and the corresponding high density of energy levels below as well as above the ionization potential. Several auto-ionizing resonances have already been reported in literature [15,16]. For the identification of further candidates ensuring highest ionization Fig.…”

Spectroscopy and Kinetics of U02 Fuel Oxidation Hydrolysis and Radiolysis: Applications to Radioactive Waste Management

“…For uranium, numerous experimental measurements of the electronic spectra of the neutral atom [90] [23] exist in the literature. All these gas-phase studies of the neutral uranium atom and the +2, +3, +4 and +5 ionic species indicate that the low lying electronic transitions are predominately due to 5f to 5f electronic excitations, which are parity forbidden.…”