In addition to the up-to-date data sources described above, it is of some interest to have the basic collisional and radiative data available for a limited number of atomic transitions that give rise to nebular lines formed at low temperatures in optically thin plasmas. A widely used compilation of such data was provided by Mendoza (1983) over a decade ago. New data are now available for most of the transitions. Table 1 presents an updated and extended dataset of maxwellian averaged collision strengths, (T), the Einstein A-values, and experimental wavelengths (Å). The are tabulated at four temperatures: 5000, 10000, 15000 and 20000 K. In some instances the temperature dependent values are unavailable. The LS collision strengths may be subdivided into fine structure components in a straightforward manner according to the statistical weights if either S = 0 or L = 0 for one of the terms. This procedure is employed for available data where applicable. In Table 1 all data pertain to fine structure transitions; however, in cases where the fine structure collision strengths are not available the total LS multiplet value is listed under the FIRST fine structure transition within the multiplet, followed by blanks for the other transitions in the multiplet. Original references are marked as superscripts and should be quoted by users in literature.
The available atomic data for these and other ions far exceeds the data presented herein. Users should consult these when additional data is required. For instance, the (T) for Fe II given in Table 1 is a very small subset of the data for 10,012 transitions for the IR, O, and UV transitions calculated by Zhang and Pradhan (1994). An even larger dataset is available for Fe III. We have concentrated only on low temperatures but the original references often contain additional data at higher temperatures and at a finer temperature mesh.
It is a pleasure to acknowledge with gratitude the guidance that AKP has received from Prof. Mike Seaton for over two decades, and the continuing inspiration from Prof. Don Osterbrock. This work was supported in part by a grant from the National Science Foundation (PHY-9115057) and the NASA LTSA program (NAGW-3315).