Abstract:

 Ab initio RHF/3-21G method has been employed to study the mechanism of the bimolecular thermolysis of HNCO. The results show that this reaction is a stepwise reaction. The first step is the dimerization of HNCO to form a four-membered ring intermediate, the second step is the dissociation of the intermediate to form the products HNCNH and CO2. The calculated activation barrier for the steps are 172.55kJ•mol-1 and 83.68kJ•mol-1, respectively. It can be seen that the first step is the rate determining step, its barrier is in good agreement with experimental data (activation energy: 176.40±16.30 kJ•mol-1). The second step is a fast step, the four-membered ring intermediate can not stay as a final product. The reaction can be described as a stepwise non-synchronous reaction.

Key words: HNCO, Thermolysis mechanism, Ab initio method