Paper LXI

Radiative E1, E2, E3, and M1 transition probabilities for Fe IV

S.N. Nahar

Astronomy & Astrophysics, 2006, Vol.448, p 779

Radiative decay rates (A) and line strengths (S) are presented for a large number of electric dipole allowed (E1) and forbidden electric quadrupole (E2), octupole (E3) and magnetic dipole (M1) transitions in Fe IV. The ion is amongst the most complex iron ions and exhibits effects of strong electron correlation. It has closely spaced fine structure levels from seven configurations: 3s$^2$3p$^6$3d$^5$, 3s$^2$3p$^6$3d$^4$4s, 3s$^2$3p$^6$3d$^4$4p, 3s$^2$3p$^6$3d$^4$4d, 3s$^2$3p$^6$3d$^3$4s4p, 3s$^2$3p$^6$3d$^3$4s4d, 3s$^2$3p$^5$3d$^6$ before an energy gap could be noted. Atomic parameters are presented for multipole radiative transitions among the 1275 fine structure levels dominated by these seven configurations. A total of approximately 173 000 transitions of type E1, E2, E3 and M1 are presented, The set of intercombination and forbidden transitions complements the earlier extensive set of dipole allowed (Delta J=0, +/- 1, Delta L=0, +/- 1, and Delta S = 0) fine structure transitions in Fe IV. The results are obtained in the relativistic Breit-Pauli approximation using an updated atomic structure code SUPERSTRUCTURE. Transition probabilities are compared with the existing results and varying degrees of agreement are found. The total number of transitions presented should provide a reasonably complete set for modeling of most optical to ultraviolet Fe IV spectra of astrophysical sources.