Ab initio chemical kinetics for the reaction of an H atom with Si ₃H₈

The kinetics and mechanism for the reaction of H with Si₃H ₈ have been investigated using various theoretical, methods including CCSD(T)/6-31.1++G(3df,2p)//B3LYP/6-311++G(3df,2p), G2M(RCC2), and CCSD(T)/ 6-31.1.++G(3df,2p)//CCSD/6-31 l.+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 OfIi-Si₃H₇ and J-Si ₃H₇ products, with 3.8 (TS1) and 3.2 (TS2) kcal/mol barriers, respectively. Significantly, the hydrogen substitution of SiH ₃ and Si₂Hs groups by attacking at the central Si atom via TS3 (3.3 kcal/mol) and a terminal Si atom of Si₃H₈ from side and end on (via TS4, 4.2 kcal/mol and TS5, 6.3 kcal/mol), were found to give SiH₃ + Si₂H₆ and SiH₄ + Si ₂H₅ products, respectively. The heats of formation of Si₃H₈, n-Si₃H₇, and i-Si ₃H₇ 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.