The full-parameter geometry optimization and harmonic vibrational frequency calculations were performed on isomers of diamidodisilanes Si₂(CH₃)₂H₂N₂(C₂H₅)₄ and azocyclosilane Si₄(CH₃)₄H₄N₂(C₆H₅)₂ by means of density functional theory (DFT) at the B3LYP/6-31＋G(d) level. Some of thermodynamic properties and relatively low excitation energies were also calculated. From the theoretical investigation, it is showed that there are no large differences of their IR spectra and other thermodynamic properties between conformational isomers. The differences were observable of IR spectra and other thermodynamic properties between stereo isomers. It was found that the two split peaks of experimental vibrational spectra of Si-H bonds were due to the different stereo isomers. DFT results agree well with the experimental IR spectra from mixed isomers.

Key words: density functional theory, stereo isomer, IR vibrational spectrum