The Spectrum of Cn in the Vacuum Ultraviolet

The spectrum of the CN radical has been investigated in the Schumann region using a three-meter vacuum spectrograph in the fourth order. A hollow cathode discharge through streaming helium, to which a trace of cyanogen was added, was used as source. Three new systems of bands were found in the region 1650–2100 Å. These involve two hitherto unknown states: a 2 Σ state designated by E, which gives rise to the transitions E 2 Σ → X 2 Σ and E 2 Σ → A 2 Π, and an inverted 2 Δ state designated by J, which gives rise to the transition J 2 Δ → A 2 Π. Rotational analyses of the bands have been made and the molecular constants evaluated. The new data, although not decisive, support the higher value (8.2 ev.) for the dissociation energy of CN.