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This section gives published references with some discussion.

4.1. Electron Impact Excitation

There are three recent compilations of data sources:

1. A special issue of Atomic Data and Nuclear Data Tables entitled ``Electron Excitation Data for Analysis of Spectral Line Radiation from Infrared to X-ray Wavelengths: Reviews and Recommendations'' (57, No.1/2, May/July 1994; Ed: James Lang), contains assessments of data, up to March 1992, along several isoelectronic and isonuclear sequences. The atomic systems (and reviewers) are: H and H-like (Callaway), He and He-like (Dubau), Li and Li-like (McWhirter), Be and Be-like (Berrington), B and B-like (Sampson, Zhang and Fontes), C and C-like (Monsignori Fossi and M. Landini), N and N-like (Kato), O-like (Lang and Summers), F-like (Bhatia), Si II - Si IV and S II - S IV (Dufton and Kingston), Fe II - Fe VIII (Pradhan), Fe IX - Fe XIV (Mason), Fe XV - Fe XVII (Badnell and Moores).

2. While reference 1. concentrates on recently computed data, nearly all of the previously available data sources in literature has been evaluated by Pradhan and Gallagher (At.Data.Nucl.Data.Tables, 52, 227, 1992). A discussion of the various methods of atomic collision theory, and important atomic effects, is also given (copies are available from AKP).

3. The most recent review of excitation cross sections of Carbon, Oxygen, Iron and rare gas ions is by Tayal, Pradhan and Pindzola (in Atomic and Molecular Processes in Magnetic Fusion Edge Plasmas, Ed: R.K. Janev, Plenum 1995). The ions reviewed are: C II - C VI, O II - O VIII, Fe II - Fe VIII, Ar VII-VIII, and Kr VII.

Large-scale calculations, primarily for electron impact excitation, are in progress under the Iron Project. The results are being published in Astronomy and Astrophysics, Supplement Series (some in the main A&A journal). An up-to-date list of publications follows.

Atomic data from the IRON Project:

I. Goals and methods. D.G.Hummer, K.A.Berrington, W.Eissner, Anil K. Pradhan, H.E. Saraph, J.A. Tully, A&A 279, 298-309, 1993.

II. Effective collision strengths for infrared transitions in carbon-like ions. D.J. Lennon, V.M. Burke, A&A Suppl. Ser. 103, 273-277, 1994.

III. Rate coefficients for electron impact excitation of Boron-like ions: Ne VI, Mg VIII, Al IX, Si X, S X, Ar XIV, Ca XVI and Fe XXII, Hong Lin Zhang, Mark Graziani and Anil K. Pradhan, A&A 283, 319-330, 1994.

IV. Electron excitation of the 2Po3/2 - 2Po1/2 fine structure transition in fluorine-like ions. H.E.Saraph, J.A.Tully, A&A Suppl. Ser. (in press).

V. Effective collision strengths for transitions in the ground configuration of oxygen-like ions. K. Butler, C.J. Zeippen, A&A Suppl. Ser. (in press).

VI. Collision strengths and rate coefficients for Fe II. Hong Lin Zhang and Anil K. Pradhan, A&A (in press).

VII. Radiative transition probabilities for Fe II. Sultana N. Nahar, A&A (in press).

VIII. Electron excitation of the 3d4 (5Dj) ground state fine structure transition in Ti-like ions V II, Cr III, Mn IV, Fe V, Co VI and Ni VII. K.A. Berrington, A&A Suppl. Ser. (submitted).

IX. Electron excitation of the 2Po3/2-1/2 fine structure transitions in chlorine-like ions from Ar II to Ni XII. J.C. Pelan and K.A. Berrington, A&A Suppl. Ser. (submitted).

X. Effective collision strengths for infrared transitions in silicon- and sulphur-like ions. M.E. Galavis, C. Mendoza and C.J. Zeippen, A&A Suppl. Ser. (submitted).

XI. The 2Po1/2-3/2 fine-structure lines of Ar VI, K VII and Ca VIII. H.E. Saraph and P.J. Storey, A&A Suppl. Ser. (submitted).

In addition to the Iron Project work there are some other recent calculations, also using the R-matrix method, for important astrophysical ions. Two of these are:

O II : McLaughlin and Bell (ApJS 1994, in press) have presented analytical fits to their earlier data for Upsilon(T) for the transitions between the 11 states 2p3 (4So, 2Do, 2Po), 2s2p4 (4P, 2D, 2S, 2P), 2p34s (4P, 2D, 2S, 2P). Work on fine structure transitions is in progress.

S II : Cai and Pradhan (ApJS, 88, 329, 1993) have presented Upsilon(T) for all 378 transitions between 28 fine structure levels of the 12 lowest LS terms 3p3 (4So, 2Do, 2Po), 3s3p2 (4P, 2D, 2S), 3p23d (2P, 4F, 4D, 2F0, 3p24s (4P, 2P).

These works update previous data for the optical and the UV lines of O II and S II, with some significant changes. For example the rate coefficient for the S II lambda 1256 UV multiplet 3p3 (4So)3/2 -> 3s3p4 (4P1/2,3/2,5/2), observed by the Hopkins Ultraviolet Telescope in the Io torus, is calculated by Cai and Pradhan to be nearly a factor of two lower than the ealier results of Ho and Henry (1990), bringing the observed intensity and abundance in better agreement with observations.

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