Fine Structure in the Far Infra-Red Spectrum of NH3

Abstract

The pure rotation absorption spectrum of N${\mathrm{H}}_3$ for final state $J=11,12,13,14,15\mathrm{}$ has been examined with high resolution. A multiplet splitting is found which may be expressed by the formula $\nu =19.89J-0.00294\mathrm{}{J}^3+0.00279J{K}^2,$ where $K$ is the quantum number of angular momentum about the symmetry axis. This equation is shown to be in good agreement with the theoretical expression of Slawsky and Dennison when the potential anharmonicities are taken into account. A calculation of the permanent dipole moment is made from the absolute intensity of one absorption, giving the value 1.3×${10}^{-18\mathrm{}}$ c.g.s. e.s.u.