Extreme ultraviolet transitions of Ca XVI in solar flare and laboratory spectra

New R-matrix calculations of electron impact excitation rates for transitio ns among the 2s(2)2p, 2s2p(2), and 2p(3) levels of Ca XVI are presented. Th ese data are subsequently used, in conjunction with recent estimates for pr oton excitation rates, to derive theoretical electron density sensitive emi ssion-line ratios involving 2s(2)2p-2s2p(2) transitions in the similar to 1 55-225 Angstrom wavelength range. A comparison of these with observational data for solar flares, obtained with the Naval Research Laboratory's S082A spectrograph on board Skylab, reveals excellent agreement between theory an d observation. In addition, the theoretical ratios compare favorably with t hose measured from the TEXT tokamak plasma, for which the electron temperat ure and density have been independently determined. This provides experimen tal support for the accuracy of the atomic data, and hence line ratio calcu lations, employed in the present analysis.