Infrared absorption spectra of mixed H2O, NH3 and (CO2)-C-12/(CO2)-C-13 ice
s subjected to 1 MeV proton irradiation were investigated. The results of a
nalyses of the spectra suggest formation of carbamic acid at low temperatur
es. The stability of this compound in the solid phase is attributed to inte
rmolecular hydrogen bonding of the zwitter-ion (NH3+COO-) structure. (C) 19
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