RESUMEN
The kinetics and mechanism for the reaction of H with Si(3)H(8) have been investigated using various theoretical methods including CCSD(T)/6-311++G(3df,2p)//B3LYP/6-311++G(3df,2p), G2M(RCC2), and CCSD(T)/6-311++G(3df,2p)//CCSD/6-311+G(d,p). The results obtained by the latter method show that H abstraction from a primary Si-H bond and a secondary Si-H bond leads to the formation of n-Si(3)H(7) and i-Si(3)H(7) products, with 3.8 (TS1) and 3.2 (TS2) kcal/mol barriers, respectively. Significantly, the hydrogen substitution of SiH(3) and Si(2)H(5) groups by attacking at the central Si atom via TS3 (3.3 kcal/mol) and a terminal Si atom of Si(3)H(8) from side and end on (via TS4, 4.2 kcal/mol and TS5, 6.3 kcal/mol), were found to give SiH(3) + Si(2)H(6) and SiH(4) + Si(2)H(5) products, respectively. The heats of formation of Si(3)H(8), n-Si(3)H(7), and i-Si(3)H(7) at 0 K are predicted to be 32.3 +/- 1.2, 68.6, and 66.6 kcal/mol, respectively. These values are in good agreement with the experimental and other theoretical values. The rate constants and branching ratios for the four product channels of the title reaction have been calculated by the transition state theory with Eckart tunneling corrections over a wide temperature region of 250-2500 K. These results may be employed for simulations of catalytic and plasma-enhanced chemical vapor deposition processes of a-Si:H films.