Abstract: Twenty-three possible steady isomers of N5H5 were optimized at 6-311++G** level using the density functional B3LYP method, and tautomerisms between them were discussed. To discuss the possibility of N5H5 isomers as candiate of energetic materials, energies and heats of formation were calculated by the G3B3 method. The results indicated that chain isomers were the most stable isomers and the isomer containing a tetrazetinyl group was the most unstable isomer. The existence of N=N double bonds were beneficial to their stabilities. The formation heats of all conformers were positive, and isomer E1 had the highest formation heat. In addition, at 6-311++G** level by the B3LYP method the molar volume of N5H5 was estimated, and from the density formula: ρ=MT/Vmol, we could know that the density of E1 was the largest.

Key words: Hydronitrogen compound, Density functional theory (DFT), Relative stability, Heat of formation, Transition state