IR spectra taken after the deposition of a NH₃:CO₂ 4:1 mixture (200 nm thickness) on carbon grains at 15 K and after 4 hr of the title reaction at 80 K. Two bands related to ﹩{{\mathrm{NH}}_{4}}^{+}﹩NH₂COO⁻ are marked by asterisks. The 15 K spectrum is vertically shifted for clarity. Inset: the time dependence of the ﹩{{\mathrm{NH}}_{4}}^{+}﹩NH₂COO⁻column density calculated from the 1550 cm⁻¹ band derived from the isothermal kinetic experiments performed with NH₃:CO₂ 4:1 ices (200 nm thickness) on carbon grains at 80 K.