Vibrational assignment and potential function for t r a n s-diazene (diimide): Predictions for c i s-diazene

A revised assignment of vibrational fundamentals is developed for trans-diazene (HN=NH) and its −d1 and −d2 modifications that is consistent with all of the published spectra. The fundamental frequencies (in cm−1) for trans-diazene are: (Ag) 3128, 1583, 1529; (Au) 1286; (Bu) 3120, 1322. A seven-parameter, general valence type potential function is fit to the 18 observed frequencies of the three isotopic species with an average frequency error of 6.6 cm−1. When transformed into internal coordinate space, the theoretical potential function calculated by Perić, Buenker, and Peyerimhoff compares favorably with the empirical function. From empirical potential functions of trans-methyldiazene, trans-diazene, and cis-methyldiazene, a potential function for cis-diazene is constructed and used to predict the vibrational frequencies of this elusive substance.