The analysis of absolute spectral line intensities and intensity ratios with spectroscopic diagnostic techniques provides empirical determinations of chemical abundances, electron densities and temperatures in astrophysical objects. Spectral line intensities and their ratios are controlled by the excitation rate coefficients for the electron temperature of the observed astrophysical structure. In order to make use of the spectral data, one must have accurate values for the relevant rate coefficients. Here at the Harvard-Smithsonian Center for Astrophysics, we have been carrying out measurements of cross sections and rate coefficients for electron impact excitation (EIE) and other related collision processes for more than 25 years.

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Nigel Atkins, Larry Gardner, John L. Kohl, Richard Rosati