Critically Evaluated Atomic Data for Au IV Spectrum

The spectral investigation of the triply ionized gold (Au IV) has been carried out in the wavelength region of 500--2106 {\AA}. The gold spectra were photographed at the National Institute of Standards and Technology (NIST, 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. Our analysis is theoretically supported by the pseudo-relativistic Hartree-Fock (HFR) formalism with superposition of configuration interactions implemented in Cowan's suite of codes. Radiative transition parameters are also calculated using HFR+CPOL (core-polarization effects) model and multiconfiguration Dirac-Hartree-Fock (MCDHF) approach, and their comparisons are used to evaluate the transition rate data. All the previously reported levels of the $5d^{8}$, $5d^{7}6s$, and $5d^{7}6p$ configurations are confirmed, except one and three are newly established. The missing $^{1}S_{0}$ level of $5d^{8}$ is now established at 55277.8 cm$^{-1}$. A total of 981 observed lines (E1-type) classified to 1031 transitions, including 133 newly identified, enabled us to optimize 139 energy levels. Several astrophysically important transitions, forbidden (M1- and E2-types) lines of $5d^{8}$ and $5d^{7}6s$, are provided with their Ritz wavelengths and radiative parameters. A critically evaluated set of energy levels, observed and Ritz wavelengths along with their uncertainties, transition rates, and uniformly-scaled intensities of Au IV lines have been presented. Also, large scale atomic data to compute opacity of Au IV in the kilonova ejecta have been supplemented in this work.