Infrared Absorption Bands of Ammonia

Eight NH₃ absorption bands have been recorded in the spectral region 1.0 to 2.0{μ} with an automatic recording, prism spectrometer. The fine structure of the bands shows that they all belong to the two general types, "composite" and "double." The 1.6{μ} band is composite like the 1.97{μ} band first resolved by Stinchcomb and Barker. The intensity of the lines is very uniform, and the line spacing, 10.2 cm^-1, agrees with that of the 1.97{μ} band, 9.98 cm^-1. Bands arising from changes of the electric moment parallel to the symmetry axis are double as was found in the 3{μ} and 10{μ} bands. The doublet spacing in the 10{μ} band is 33 cm^-1, but only 1.6 cm^-1 in the one at 3{μ}. D. M. Dennison has shown that the doublet spacing should rapidly decrease in the higher levels, and for harmonic bands the separation should be so large that they would not appear double. The 1.51{μ} and 1.22{μ} bands both appear as double, and have a separation of 30.3 cm^-1 and 30.4 cm^-1, respectively. Evidently the multiplicity of some of the higher levels is more evident than the present theory predicts.