The Ultraviolet Absorption Bands of Ammonia

The ultraviolet absorption bands of ammonia have been investigated in the region from 2400 to 1900A over a wide range of temperatures and pressures. The frequencies of a number of intense double-headed bands have been measured and an analysis of these bands is presented. The doublet separation is nearly constant and is equal to 70 cm^-1. Only two fundamental frequencies are observed in the upper state, namely, 890 and 2720 cm^-1. The predissociation which occurs in the excited state is discussed and accounted for by assuming that the ν₂^'(⊥) type of vibration of the molecule is always unstable.