Knowledge Bank

When the ammonia dimer, $(NH3)2$, had been measured in the microwave region1 for the first time, only the G states (group G%), $k=0$, were observed. All lines showed a rather complex 14N quadrupole hyperfine structure. Combined with dipole moment measurements Klemperer et al. proposed the ``cyclic structure'' which was in disagreement to former ab initio theories predicting the hydrogen bonded structure. New $measurements2,3$ demonstrated, that $(NH3)$, exhibits large amplitude motions. A structural determination in other tunneling states is therefore of special interest. Dipole moment measurements carried out at the tunable FIR spectrometer in Nijmegen gave for the $G(G12)k=1$ state a surprisingly small dipole moment. Using the pulsed Molecular beam microwave Fourier transform spectrometer in Kiel the hyperline structure in the $J=2-1E3/E4(G13,G41)$ states could be fully resolved. These measurements should help in understanding the structure of ($NH3)2$.