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The expressions for the hyperfine structure separations and the relative intensities in the ammonia inversion spectrum are derived with quantum mechanics under the assumption that the splitting is caused by the interaction of an electric quadrupole moment of the N^14 nucleus with the electric charge distribution in the rest of the molecule. Furthermore, we consider the displacement of the absorption lines in an electric field E of variable strength. General formulas for the positions of energy levels for weak (EE₂) fields (E₂500 volt/cm) are given and the methods outlined for obtaining solutions of the secular equation for intermediate fields (EE₂). The intensities and selection rules for longitudinal and transverse transitions are determined and one particular case (J=K=3) is worked out in detail.
J. M. Jauch (1947) studied this question.