The infrared and Raman spectra of ethylenediamine and its deuterated derivatives have been studied in both the liquid and solid states. An assignment of the fundamental vibrational modes for the four molecules is proposed assuming for the liquids a gauche configuration (Cz symmetry); the assignment is based on depolarization values, isotopic shifts and classic group frequencies correlations. fNTRODUCTION Ethylenediamine (En) is a much-used compound in co-ordination chemistry, because of its ability to give rise to complexes in which it is present as a bidentate ligand.The complexes that are obtained with various metals all have a structure such that the En-metal system constitutes an almost planar pentagon with a pseudo-cis configuration for the NCCN skeleton of the En molecule .I In the solid state,' the molecule takes on a trans configuration and has two crystalline forms of which, the one that is stable below 200 K, still maintains a centrosymmetric molecular structure, but seems to have less freedom of movement as regards the internal rotations of the NH2 groups. This interpretation was proposed some years ago by Righini and Califano3 on the basis of a detailed study of the vibrational spectra of the two crystalline forms.In the gaseous state, Yokozeki and Kuchitsu4 have shown, by using an electron diffraction technique, that the molecule possesses conformational isomerism and that the prevalent form (more than 95%) is the gauche conformer with a dihedral angle of 63", measured with respect to the cis configuration; this gives the molecule Cz symmetry. As regards the geometry and consequent molecular symmetry of En in the liquid state (which is the stable physical state at room temperature) there still exists some uncertainty. Some years ago Shimanouchi' demonstrated spectroscopic evidence for a gauche conformation for this molecule in the liquid state, but no subsequent author has taken this point of view. A complete assignment of the liquid ethylenediamine vibrational spectrum, based on this interpretation of its molecular structure, is, to the best of our knowledge, still lacking. The study that had behen previously carried out by Borring and Rasmussen, based solely on an analysis of the infrared spectra of the four deuterated species of En, does not appear to lead to the definitive assignment for the normal vibrations of this molecule since the infrared spectrum was too complex and in any case lacked the necessary detail in the 1100-700 cm-I range where, from classical group frequency considerations, the absorptions of a great number of the fundamental modes of this compound are predicted to fall.The vibrational assignments that had previously been made for the liquid phase were all based on a cis structure, with consequent C2u molecular ~y m m e t r y .~-~ However, the selection rules predicted for this symmetry do not seem to be obeyed if the behaviour of the vibrational spectrum of En in the liquid state is taken into consideration. Of the 30 normal modes of the molecule, only 24 should be active in th...

Resonance Raman excitation profiles of some azo dyes were studies and interpreted in terms of a model that treats vibrations as displaced harmonic oscillators. It is shown that the visible absorption spectrum is formed by two overlapping electronic transitions of a mixed chargetransfer and nx* character.

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Resonance Raman spectra and excitation profiles are reported for six azo dyes in CCI, solutions through the visible absorption spectrum region. The excitation profiles observed for the five most intense fundamentals in each dye indicate interference between two overlapping electronic manifolds.