Anomalous Values of Certain of the Fine Structure Lines in the Ammonia Microwave Spectrum

Abstract

The anomalous positions in the microwave spectrum of ammonia of the lines originating with the rotational levels $K=3\mathrm{}$ are explained on the basis of a $K$-type splitting of these levels. The splitting is due to a fourth-order perturbation originating with the first-order correction terms to the moments of inertia, ${I_{\mathrm{xx}}}^{\mathrm{}\left(e\right)\mathrm{}}={I_{\mathrm{yy}}}^{\mathrm{}\left(e\right)\mathrm{}}$, and the first-order coriolis correction terms. The Pauli exclusion principle permits only one of the two components to be present. Thus in the lower vibration state when $J$ is even only the lower component of the levels $K=3\mathrm{}$ is present, but when $J$ is odd only the upper component is permitted. Similarly, for the upper vibration state when $J$ is even only the upper component of the levels $K=3\mathrm{}$ may exist while for $J$ odd only the lower component may exist. Since in this spectrum $\Delta J=\Delta K=0\mathrm{}$, the lines originating in levels where $J$ is even will be displaced to shorter wave-lengths, while the lines originating in levels where $J$ is odd will be displaced to longer wave-lengths. The agreement between computed shifts and measured shifts is satisfactory.