Energy Levels and Electric Dipole Transitions for Neutral Actinium (Z = 89)

Abstract

We have reported a relativistic multiconfiguration Dirac-Fock calculation including Breit and quantum electrodynamic contributions on the level structure of atomic actinium, Ac I (Z = 89). The computations have been carried out for the low 45 even and 60 odd-parity levels, and the electric dipole transition parameters (wavelengths, oscillator strengths and transition probabilities) for some transitions between these levels. Comparison has been also made with other results in available literature.

Calculations of the atomic structure for the low-lying states of actinium

“…As noted, it is possible that a number of these levels have been previously misidentified in the literature. The three largest deviations from experiment are likely explained by misidentification of the levels [3,10], see footnotes of Table I. In Ref.…”

“…The data for the electron spectrum of Ac presented in the NIST database [1] miss many levels and there are indications that some of the data are not accurate [2], see also Refs. [3][4][5].…”

“…Ref. [3]), and are likely accurate to the few-percent level for the energy levels, and to around 10% for most transition matrix elements. Newer experimental work may indicate that some of the levels may have been previously misidentified (e.g., [2,4,[10][11][12]).…”

Detection of missing low-lying atomic states in actinium

“…The atomic structure of actinium was elucidated by Judd who calculated the ordering and properties of lowlying levels of actinide atoms [12]. This work was extended by calculations of energy differences between the lowest states [13] and a prediction of the parameters of electric-dipole (E1) transitions in actinium [14] using the Hartree-Fock method, as well as other theoretical studies [15][16][17][18][19].…”

“…4(b) were calculated through a hybrid approach that combines configuration interaction (CI) with a linearized coupledcluster method that includes single and double excitations (CI+LCCSD) [34,35]. Using the nuclear magneticdipole moment µ = 1.07 (18)µ N , where µ N is the nuclear magneton, and the spectroscopic electric-quadrupole moment Q = 1.74 (10)…”