The structures of CH₃NO isomers and their isomerization have been investigated at CCSD(T)/ 6-311＋＋G(d,p)//B3LYP/6-311＋＋G(d,p) level. 23 isomers including CH₃NO were found and they were linked by 24 transition states. The characterizations of the transition states are confirmed by vibration analysis. The intrinsic reaction coordinates (IRC) have been traced according to Fukui s theory and the connecting relationship of the transition states with the reactants and products was confirmed. The calculated results show that the isomers with N—C—O structure are the most stable, while those with C—O—N and C—N—O structures are not stable because of their high energies. The isomers transform to each other by the rotation of the chemical bond, the transfer of H atom, the reorganization of C, N and O skeleton and the mixed type reaction mechanism of above-mentioned.

Key words: CH₃NO, isomerization, transition state, reaction mechanism