Two types of infrared spectra observed during the formation of ammonium carbamate [Formula: see text] from the reaction of NH 3 and CO 2 in the solid state at low temperatures have been re-examined. These spectra had been assigned previously to amorphous and crystalline ammonium carbamate but the present data suggest their origins to be [Formula: see text] and its unstable precursor (NH 3 ) 2 CO 2 in which CO 2 is bent. Spectra of amorphous and crystalline ammonium carbamate have been distinguished by comparing the systems NH 3 /CO 2 and NH 3 /CO 2 /H 2 O. Hydrogen ion transfer in the diammoniates occurred at about −80 °C for NH 3 /CO 2 and about −40 °C for ND 3 /CO 2 .
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C. Hisatsune (1984) studied this question.