Next Contents


In a pioneering study on the electron impact excitation of atomic oxygen, Seaton (1955) formulated the now well known close-coupling approximation of atomic collision theory, which he termed the ``continuum state Hartree-Fock method'', reflecting the physical picture that the new method was an extension of the bound state method to the continuum region that encompassed electron-ion scattering and photoionization phenomena. For nearly three decades, the close coupling approximation has been widely employed to calculate the most accurate low-energy cross sections for excitation and photoionization, and radiative transition probabilities. Large computational packages were developed, mainly at University College London and the Queen's University of Belfast, to carry out the enormous task of fulfilling the needs of astrophysicists and plasma physicists. In particular, the R-matrix method developed by Burke and associates (Burke et al. 1971) has proved to be computationally very efficient for large-scale calculations.

A huge amount of radiative atomic data was produced, during last 10 years or so, under the auspices of an international collaboration of atomic physicists and astrophysicists, called the Opacity Project, led by Seaton (Seaton et al. 1994). Photoionization cross sections and oscillator strengths were calculated using the R-matrix method (Seaton 1987, Berrington et al. 1987) for almost all astrophysically abundant elements in various ionization stages. The calculations were carried out for LS multiplets; fine structure was not considered as it is relatively less important for the calculation of stellar opacities, which was the express aim of the Project. Recently, employing the basic tecniques of the Opacity Project and new developments incorporating relativistic effects into the R-matrix method, a new project called the Iron Project has been initiated (Hummer et al. 1993) that aims to compute accurate cross sections for electron impact excitation of most astrophysical ions including fine structure. The main aim of the Iron Project is the calculation of precise atomic data for the Iron group elements that are astrophysically very important but for which little reliable data is presently available. Thus the Opacity Project and the Iron Project are now providing much of the atomic data needed by astronomers.

This report consists of a review of data sources for:

For completeness, data sources are also given for line broadening, recombination lines, electron impact ionization, charge exchange, proton impact excitation, isotopic and hyperfine structure, and energy levels and wavelengths. With the exception of energy levels, very little of the data is experimental; we confine ourselves mainly to a discussion of the theoretical data. A general bibliography for most of these atomic processes has been presented by Butler (1993). More up-to-date data and information on the Opacity Project, the Iron Project, and related work may be obtained from the Website.

The prominent spectral lines in nebular astrophysics are mostly due to forbidden transition among low-lying levels of atomic ions. In an attempt to update and extend the extremely useful compilation by Mendoza (1983) more than a decade ago, recommended data for electron impact excitation and transition probabilities for emission lines in AGN's, nebulae and other sources are tabulated.

Next Contents