1 Introduction

Accurate atomic data for iron and other iron group elements is of major importance in astrophysics. Among these elements, nickel is the second most abundant element after iron. Then, reliable modeling of the spectra of this element and determination of its abundance have direct implications on our understanding of the chemical evolution of the universe. In particular, singly ionized nickel is often detected in studies of absorption lines in the diffuse ISM. Ni II is also a common source of emission lines in the spectra of H II regions, novae, supernovae, and supernova remnants. Despite of the importance of nickel in astrophysics very few studies of the atomic data for this element have ever been carried out. Consequently, there are at present great uncertainties on the gas phase abundances of nickel which reach up to orders of magnitude (e.g. Haas et al. 1996; Oliva et al. 1988; Henry & Fesen 1988).

The IRON Project is an international collaboration devoted to the computation of accurate atomic data for iron peak elements (Hummer et al. 1993). A complete list of papers including those in press can be found at http://www.am.qub.uk/projects/iron/papers/, where abstracts are also given for each paper. In the present paper we report extensive radiative data for Ni II. The data sets include multiplet energy levels, dipole allowed transition probabilities, and total and partial photoionization cross sections including detailed resonance structures.