A REVIEW OF ELECTRON-IMPACT EXCITATION DATA FOR THE BERYLLIUM ISOELECTRONIC SEQUENCE (Z = 4 TO 28)

Each beryllium-like ion is considered in tum, from Z = 4 to 28 (Be I to Ni XXV). References are given for the main electron impact excitation calculations perform (for example, Coulomb-Born, distorted-wave, and R-matrix calculations), in chronological order, noting whether tabular data (for example, collision strengths, rates, fits) are available. Comparisons of the thermally averaged effective collision strengths are made for three DELTAn = 0 and one DELTAn = 1 sample transitions for the even-charged ions. The most accurate data come from large R-matrix calculations which explicitly include configuration interactions, resonances, channel coupling associated with n less-than-or-equal-to 3 states, and, at higher Z, relativistic effects. Only a few ions have been treated in such a sophisticated way; further work will therefore be necessary if reliable data are required across the isoelectronic sequence. Recommendations are made for the best data currently available for each ion. (C) 1994 Academic Press, Inc.