Paper XXXIX

Photoionization cross sections and oscillator strengths for Ni II

M.A. Bautista

Astronomy & Astrophysics Supplement Series, 1999, Vol.137, pp.529-535

We present calculations of energy levels, photoionization cross sections and dipole allowed transition probabilities for singly ionized nickel. The computations were carried out in the close coupling approximation using the R-matrix method including 49 LS terms with multiplicity $(2S+1)=1,3$ and 5 of the target ion Ni III. We calculated 836 LS states, 561 of which are bound with principal quantum number $n\le 10$ and angular momentum $L\le 7$. The results also include dipole oscillator strengths 23738 LS transitions, and photoionization cross sections with detailed resonance structures for all bound states. The f-values and radiative lifetimes agree well with available experimental measurements. However, the present f-values disagree considerably from previous computations by Kurucz and coworkers which are currently used in Ni II abundance determinations of the ISM. In particular, the Kurucz f-values for transitions from the Ni II ground state seem to be overestimated by factors of two to three thus, nickel may be less depleted in ISM than previously estimated. The photoionization cross section for the 3d$^9$ $^2$D ground state of Ni II exhibits near threshold packs of resonances that rise over the background cross section by several orders of magnitude.