Radiative decay rates for magnetic dipole (M1) and electric quadrupole (E2) transitions between low-lying levels within the 4f3 ground configuration of Pr III

Abstract A new set of theoretical radiative decay rates characterizing forbidden transitions in doubly charged praseodymium (Pr III) is reported in the present paper. More precisely, transition probabilities were computed for all magnetic dipole (M1) and electric quadrupole (E2) lines involving the lowest energy levels of the 4f$^3$ ground configuration located below 20000 cm$^{-1}$ since the levels above this limit are preferentially depopulated by allowed electric dipole (E1) transitions. The calculations were carried out using different computational strategies based firstly on the pseudo-relativistic Hartree-Fock (HFR) method and secondly on the fully relativistic Multiconfiguration Dirac-Hartree-Fock (MCDHF) method. The comparison between the results obtained by these independent approaches makes it possible to estimate their reliability. Comparisons with the few previously published data were also made. In addition, some astrophysical implications were deduced from the new atomic parameters computed in the present work, such as the possible presence of [Pr III] lines in the infrared spectra recorded by the {\it James Webb Space Telescope} ($JWST$) in the context of the investigation of kilonovae in their nebular phase, i.e. several days after neutron star mergers.