The spin–spin coupling constants in the ammonia dimer

The indirect spin–spin coupling constants have been calculated by means of the linear response MCSCF method for the three stationary points of the (NH3)2 dimer. The obtained intermolecular coupling constants and the dimerization-induced changes of the intramolecular coupling constants are compared with the results for the (HF)2 and (H2O)2 complexes and discussed as parameters of the hydrogen bond. The best correlation with the strength of the X–H⋯Y hydrogen bond is exhibited by the dimerization-induced change in the reduced intramolecular 1K(XH) coupling. The reduced hydrogen-bond-transmitted 1hK(YH) coupling constant also correlates to some extent with the interaction energy. No correlation with the interaction energy has been found for the reduced 2hK(XY) coupling constant. The intermolecular coupling constants in (NH3)2 seem to be determined primarily by the internuclear distances.