| Abstract
| - The kinetics of the reversible decomposition of ammoniumcarbamate, NH4CO2NH2(AC), into NH3 (A) andCO2 (C) has been studied between 278 and 312 K by recordingthe time dependence of the total pressureabove an AC sample that, after being previously evacuated, is exposedto the headspace of an isoteniscope.At early times (<1 s), the data show an inflection, which isenhanced in first derivative transformations.Three mechanisms are discussed, each containing six rateconstants. Two assume the presence of gas phasecarbamic acid (CA) as an intermediate. These mechanisms areexplored further through ab initio computationalstudies of CA. These results indicate that gas phase CA is a verystable species. No evidence could befound for its presence from Fourier transform IR spectra of theequilibrium vapor above AC. The mechanismthat we suggest involves the reversible decomposition of AC intosurface-bound CA, A, and C molecules,with the latter two reversibly desorbing from the surface. Theexperimental kinetic data are consistent withall three mechanisms. The rate data do not contain sufficientinformation to allow all rate constants to beuniquely determined. Simulation studies are used to demonstrateconsistency of the mechanisms with thedata.
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