Microwave anticrossing spectrum of ammonia

A microwave spectrometer designed to make precision Stark measurements at high electric fields has been used to study the inversion spectrum of ammonia. An avoided crossing has been measured between the lower member of the inversion doublet for (J=13, K=11) and the upper member of the (14,14) doublet. The two parameters that characterize the anticrossing are the zero-field splitting Δ0 between the levels and the distortion dipole moment μD that provides the (ΔJ=±1, ΔK=±3) mixing. For a number of other (J,K) values, a detailed study of the Stark effect has been carried out to determine the dipole distortion constants μJ and μK which appear in the effective dipole moment μQ(J,K) that provides the (ΔJ=0, ΔK=0) mixing between members of the same doublet: μQ=μ0 +μJJ(J+1) +μKK2. From a simultaneous fit to the anticrossing and conventional measurements, it has been determined that: Δ0=678.70(20) MHz; ‖μD‖ =124.1(7.0) μD; μJ =177.5(3.0) μD; and μK =−348.5(3.0) μD. The signs of μJ and μK are specified relative to that of μ0. The values of μD, μJ, and μK are discussed in the light of centrifugal distortion theory; the current measurements of μJ and μK are compared to the recent laser-Stark determinations of Ueda and Iwahori. By using the molecular beam results of Marshall and Muenter, values have been obtained for μ0 and for the static anisotropy in the polarizability.