Extension of Series in the First Spectrum of Indium (In I)

The ultra-violet absorption spectrum of indium vapour has been photographed by means of a 3-metre grating spectrograph. Lines of the series 5 2 P 1/2 0 - n 2 S 1/2 ( n =9 to 27), n 2 D 3/2 ( n =7 to 33), 5 2 P 3/2 0 - n 2 S 1/2 ( n =10 to 29), n 2 D 3/2 ( n =8 to 19), n 2 D 5/2 ( n =8 to 34), have been measured against good wavelength standards. A short sixth series is identified as 5 2 P 1/2 0 - n 2 P 1/2 0 . The accepted value for the ionization potential has been confirmed. From a consideration of the character of the perturbations in the n 2 D series we conclude that the sp 2 2 D term lies above the ionization limit, instead of, as formerly supposed, below.