Theoretical studies of termolecular thermal recombination of silicon atoms

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Abstract
Termolecular recombination of silicon atoms in the presence of an atomic third body M is studied for thermal reactions on the ground-state 3Σ−g potential curve for Si2 dimers. The total potential surface is assumed to have pairwise form with the Si2 term being a Morse potential fitted to multireferenced double-excitation, configuration interaction (MRDCI) results. Lennard-Jones (LJ) (12,6) potentials are used for the two M–Si interactions. The termolecular rate coefficients for the temperature range 200≤T≤300 K are found to be in the range 1.69×1015≤kr(T) ≤2.56×1015 cm6/mol s if a statistical factor of unity is employed. It is argued that the most appropriate statistical factor is 1/9 for which the rate coefficients fall in the range 1.88×1014≤kr(T) ≤2.85×1014 cm6/mol s. The statistical error in the calculation precludes an accurate calculation of the small activation energy for the recombination. The limiting values are −1.24≤Ea ≤2.32 kcal/mol with a least-squares result of Ea =−0.028 kcal/mol.