Term Analysis of the Third Spectrum of Iron (Fe Iii).

The Fe In spectrum has been measured in the region from approximately 500 A to 6500 A, and its analysis has been carried as far as the observational data permit. Of the 34 theoretically possible terms of the 3d6 configuration, 32 have been found, the 2 high iS and `D terms being the only missing ones. Of the 74 theoretical levels for 3d5 4s, only 10 high-lying levels1' 3(SPD) have not been found. Of the configuration 3d5 4p, practically all theoretically possible levels corresponding to those found of 3d5 4s have been established. The final tables contain 320 levels and approximately 1500 classified lines. The permitted and forbidden transitions of Fe in play an important role in a wide variety of stellar and nebular spectra. INTRODUCTIO