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 ${\mathrm{cm}}^{-1\mathrm{}}$. Only two fundamental frequencies are observed in the upper state, namely, 890 and 2720 ${\mathrm{cm}}^{-1\mathrm{}}$. The predissociation which occurs in the excited state is discussed and accounted for by assuming that the ${{\nu }_2}^{\prime }\left(\perp \right)$ type of vibration of the molecule is always unstable.