Carbonylation of ammonia by gaseous FCO+.: A G2 and Rice-Ramsperger-Kassel-Marcus study of the detailed mechanistic aspects

The detailed mechanism of the gas-phase carbonylation of NH, by FCO+ with formation of H2NCO+ and HF has been theoretically investigated by G2 and Rice-Ramsperger-Kassel-Marcus (RRKM) calculations. The results provide a coherent description of the experimental evidence, so far obtained by Fourier transform ion cyclotron resonance spectrometry. The detailed G2 potential energy surface of the reaction has been used to outline the corresponding kinetic scheme, whose rigorous formulation has been simplified by making assumptions based on the explicit evaluation of all the involved kinetic constants, calculated according to the RRKM theory. It was possible to estimate the efficiency of the reaction for different alternative mechanisms and to compare the obtained values with the experimentally measured efficiency, used as a probing reference value. The obtained results indicate that the reaction occurs by a "composite" mechanism, which involves the initial formation of an adduct between FCO+ and NH3 and the subsequent loss of HF by two distinct paths. In addition, it was possible to conclude that the only ionic product expected from the reaction is the H2N-CO+ isomer. (Int J Mass Spectrom 184 (1999) 89-101) (C) 1999 Elsevier Science B.V.