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The dicyanamide or dicyanimide ion (NsaC-N-C=N)-is isoelectronic with carbon suboxide and therefore might exist + in a linear resonance form (N-=C=N=C=N-) having the same double bond array as the latter. A comparison of the infrared with Raman spectra should show at once whether this ion is linear or bent, since the linear form would have a center of symmetry and there would therefore be no coincidence in absorption between the two types of spectra.The IR spectrum of this ion has been investigated at the American Cyanamide Corporation laboratories [1], and since this work was completed, Kuhn and Mecke [2] have reported the IR spectra in the NaCI and KBr regions of a number of salts. Since quite low values for bending frequencies for nitrile compounds have been reported [4][5][6], and the Raman spectra of a solution of the sodium salt showed indications of a broad line at 170 cm -1, the infrared measurements were carried out to 100 cm-1 on the instrument at MIT built by Lord and Mc Cubbin [7].EXPERIMENT AL Sodium dicyanamide was the principal salt used in this investigation. Two samples were prepared: one from sodium cyanamide and cyanogen bromide according to the method of Madelung and Kern [8] and the other from zinc dicyanamide kindly supplied by the American Cyanamide Corporation. The spectra of the two samples were identical.Infrared spectra in the CaF 2, NaCI, and KBr regions were run on a Baird Associates Model A double-beam instrument using both nujol mulls and KBr pellets. For the spectra at frequencies below 425 cm-1 , the sodium dicyanamide was dispersed in polyethylene.