The Inversion Spectrum of Ammonia

Ammonia gas is known to exhibit a strong absorption in the region of 0.8 ${\mathrm{cm}}^{-1\mathrm{}}$. By sweeping the frequency of a continuous wave oscillator and using a balanced wave guide system with one arm of the wave guide serving as an absorption chamber, thirty lines of the fine structure, as predicted by Sheng, Barker, and Dennison, have been observed in this region. Their intensities and frequencies have been measured for two different temperatures and an empirical expression for the frequencies of the lines in terms of their rotational quantum numbers is given. At pressures of 5×${10}^{-1\mathrm{}}$ mm Hg and below, the lines are very well resolved. At pressures of ${10}^{-2\mathrm{}}$ mm Hg and below, a definite hyperfine structure appears. The Stark effect is also observed when a d.c. field is applied to the absorbing gas.