Ab initio study on isomerization reaction of the CH5N2+ cation

Ab initio molecular orbital calculations with a split-valence plus polarization basis set have been used to study the structures of the observed isomers of the CH5N2+ cation: CH3-NH=NH+ (1), CH3-N=NH+2(2), CH2=NH-NH2+ (3) and CH2=N-NH3+ (4), and the isomerization reactions between them. Isomer (3) is the most stable structure of the CH5N2+ cation, and isomers (1), (2) and (4) lie 12.3, 10.6 and 5.9 kcal mol(-1), respectively, above (3) in energy. From the rate constants, calculated with a simple transition state theory, it is predicted that the isomerization reactions of the CH5N2+ cation are difficult under normal conditions. The bridged structure between isomers (3) and (4) which was proposed by Burgers is confirmed to be a first-order saddle point at both the HF/6-31G* and MP2/6-31G* levels.