Description:
<jats:p>The general valence force field for the in-plane motions of diimide has been determined from a total of 24 vibrational frequencies of HNNH, HNND, DNND, and 15N substituted counterparts. The unusual upward shifts observed for the NN stretching frequency on deuteration can be obtained when these shifts are directly constrained, but an exact fit was not possible due to convergence problems. Most of the force constants are well determined and a comparison is offered with recent results for CH3NNH, CH3NNCH3, FNNF, and C2H4. The latter force fields suggest that the unobserved torsional frequency of HNNH should lie above 1300 cm−1 and hence this spectral region has been carefully reexamined.</jats:p>