THEORETICAL STUDY ON THERMODYNAMIC PROPERTIES AND STABILITIES OF N-SILANES

First-principle computations were performed on the n-silane series (SinH2n+2, n = 1-10). The heat of formation (Delta H-f), Gibbs free energy of formation (Delta(f)G), bond length, and bond dissociation energy (BDE) for both the Si-Si and Si-H bonds were predicted. The values of Delta H-f and Delta(f)G from the accurate high level G3 method for lower silanes (n <= 5) were compared with experimental values and used as benchmarks. Thermodynamic properties derived from the G3 method in combination with the permutation reaction are in better agreement with experiments than those with the atomization reaction. The increments of the Delta H-f and Delta(f)G values with an increasing SiH2-unit for n-silanes are 40.39 and 58.93 kJ/mol on average, respectively. The length of Si-Si bond increases slightly on average as the series number increases and then tends to be a constant for higher silanes. The BDEs for both the Si-Si and Si-H bonds initially decrease for lower silanes, and then approach a constant for higher silanes. The BDEs of the Si-Si bonds are smaller than those of Si-H bonds. The higher silanes are more unstable than the lower silanes. The average BDE of Si-Si bond at the MP2 level is ca. 302 kJ/mol, which is only half the experimental BDE value of the C-C bond (618 kJ/mol).