Emission bands of halogens
Among the diffuse fluctuation bands observed in the emission spectrum of iodine, there are five groups each of which involves a frequency difference of about 165 cm.−1 among the component bands. An interpretation of these five groups is given, which shows that they are due to transitions from a common initial level to five different final levels. The initial level is identified with the newly discovered level 0 u + at 51683 cm−1. The five different final levels are identified with just those states whose energies and nature can be calculated theoretically. All these are repulsive states with potential energy curves of varying slopes. The occurrence of bands (3945·6 and 3919·4 A) in the second group and of bands (3879·9 and 3855·8 A) in the third group clearly shows that the coupling conditions in I2 are of Hund’s case (c).