Measurement of the Fe VIII-Fe XVI 3-3 Emission in the Extreme Ultraviolet and Comparison with CHIANTI

Laboratory measurements of the n = 3 to n = 3 emission from M-shell iron ions are presented and compared to synthetic spectra from the CHIANTI spectral model. The measurements cover the range 170-290 Å and are made at an electron density of about 10¹¹ cm^-3. Emission from Fe VIII through Fe XVI has been identified. Excellent agreement with CHIANTI predictions is found for most lines. Twenty weaker features are noted in the laboratory data that are either absent in CHIANTI or have recently been added and correspond to lines that have not been verified by experimental measurements. A few of these lines may have already been observed (but not yet identified) in the Sun. The features are attributed to emission from various charge states of iron, notably Fe IX and Fe XIII, and two features have been identified as transitions in Fe VIII, i.e., the 3p ⁶3d ² D _5/2-3p ⁵3d ^{2 2} P _3/2 and the 3p ⁶3d ² D _3/2-3p ⁵3d ^{2 2} P _1/2 transitions at 225.25 ± 0.12 and 226.35 ± 0.10 Å, respectively. Seven lines in Fe XI, Fe XII, and Fe XIII between 200 and 205 Å are noted for which the wavelengths in the CHIANTI database disagree with those in the current database of the National Institute of Standards and Technology. Our measurements of five of these lines appear to agree with the assignments used in CHIANTI.