The Microwave Spectra of the Deutero-Ammonias

Measurements of the inversion-rotation spectra of the deutero-ammonias have been made in the 4000-Mc/sec to 80,000-Mc/sec region. Fifty lines of N${\mathrm{H}}_2$D and NH${\mathrm{D}}_2$ have been measured and identified by means of the Stark effect. As expected, our results show that for these molecules, only simultaneous rotational and inversion transitions can be observed. Thus, corresponding to each $J_{\tau }\to J_{{\tau }^{\prime }}$ transition two absorption lines can be observed, separated by either twice the rotational energy separation or twice the inversion splitting of the levels involved. From our observations the inversion splittings of the partially deuterated molecules can be calculated and are found to be in good agreement with the Dennison and Uhlenbeck inversion doubling theory. Thus, the inversion splittings for the ammonia molecules are approximately as follows: 24,000 Mc/sec for N${\mathrm{H}}_3$; 12,000 Mc/sec for N${\mathrm{H}}_2$D; 5000 Mc/sec for NH${\mathrm{D}}_2$; 2000 Mc/sec for N${\mathrm{D}}_3$. Our results are also in agreement with the structural parameters of ammonia as given by Herzberg. The sign of the nuclear quadrupole coupling constant was also measured and found to be negative, as expected. The centrifugal distortion for both rotation and inversion states has been experimentally determined.