A New Band System of the C₂ Molecule.

Five new bands in the spectrum of the C2 molecule have been discovered in the laboratory, with heads at XX 7715, 7908, 8108, 8751, and 8980. They are all degraded to the red. An analysis of the bands has shown that they are due to a 1ll~_1~ transition. The two electronic states involved in the transi- tion are the lower states of the 1ll~~1ll~ Deslandres-D'Azambuja system and the 1~_1~ Mulliken system. The excitation energy, P~o, of the `IL~ state relative to the ir state is 8268.50 cm' (1.025 e.v.). Improved molecular constants for the two states are given in Table 6