Revised and extended analysis of doubly ionized gold: Au III

Abstract

The spectrum of doubly ionized gold (Au III) photographed in the region 450–2106 Å has been investigated. The gold spectra have been recorded at two places viz. at the National Institute of Standards and Technology (USA) on a 10.7-m normal incidence vacuum spectrograph (NIVS) using a sliding spark source as well as on a 3-m NIVS at the Antigonish laboratory in Canada with a triggered spark source. Au III has a ground configuration [4f14]5p65d9 with 2D5/2 as its lowest level. Excited configurations are quite complicated as the first excited odd parity configuration 5d86p alone contains 45 energy levels. Excitation of a single electron from the valence 5d shell produces configurations of the type 5d8nl. Various configurations arise due to multiple excitation of the 5d9 subshell, e.g., 5d76s6p, 5d76s2, 5d66s26p, 5d76p2, etc. Theoretical predictions were made using Cowan's quasi-relativistic Hartree-Fock code with the superposition of configurations involving 5p6 [5d9 + 5d8ns (n = 6–8) + 5d8nd (n = 6–8) + 5d76l2(l = 0–2)+5d7(6s6d+ 6s7s+ 6d7s)] in the even parity system and 5p5 [5d10 + 5d96s] + 5p6 [5d8np (n = 6–8) + 5d8nf (n = 5–7) + 5d7 (6s6p+ 6s7p+ 6p7s+ 6p6d+ 6s5f+ 6s6f) + 5d66s26p] in the odd parity matrix. A total of 262 energy levels belonging to the 5d9 + 5d8[6s+7s+6d+6p] + 5d7[6s2 + 6s6p] configurations have been established, 69 being new including three revised levels, one from each of the 5d86d, 5d87s and 5d76s6p configurations. In the process, 1504 spectral transitions have been classified in the wavelength region 570–3310 Å. The accuracy of the wavelength measurements for sharp and unblended lines is ±0.005 Å. The final interpretation of the results was made on the basis of least squares fitted parametric calculations. The level optimization was achieved with a computer program LOPT.