The Spectrum of Singly Ionized Atomic Iodine (I ii)

The I ii spectrum has been excited in electrodeless lamps and photographed from 655 A to 11084 A. Wavelengths and estimated intensities are given for almost 2,400 lines. A revision and extension of the earlier analyses of this spectrum has increased the number of known even levels from 43 to 124, and the number of odd levels from 55 to 190. New g_J-factors are given for 46 levels, and the previous designations of 40 levels are changed. Improved measurements in the vacuum ultraviolet region give a correction of 7.4 cm⁻¹ to be subtracted from the values listed in Atomic Energy Levels, Vol. 3 (1958), for all levels above the ground configuration. The approximately 1,800 classified lines now include all of the strongest lines. The ¹S₀ of the ground configuration 5s²5p⁴ has been found, and this configuration has been fitted to intermediate coupling theory. Magnetic dipole transitions between levels of the ground configuration, ³P₂–¹D₂ (7282 A) and ³P₁–¹S₀ (4460 A), have been observed and their nature confirmed by the Zeeman effect. The line 5p^{4 3}P₂–¹D₂ shows hyperfine structure which is in approximate agreement with a theoretical calculation of the expected structure. New levels have been found for almost all higher configurations. All previously known series have been extended and new ones found. From one of the new series, 5p3(4S°)5−12g5G6°, the principal ionization energy for I ii (154304 ±1 cm⁻¹) has been derived. The results of the analysis are compared with theoretical expectations in a number of cases.