Kinetics of substituted silylene addition and elimination in silicon nanocluster growth captured by group additivity

Accurate rate coefficients for 40 bimolecular substituted silylene addition reactions for silicon hydrides containing up to nine silicon atoms are calculated using the G3//B3LYP method. The overall reactions exhibit two steps: the reactants first meet to form an adduct, which then converts into a saturated silicon hydride. Values for the single-event Arrhenius pre-exponential factor, Ã, and the activation energy, E_a, are calculated from the G3//B3LYP rate coefficients corrected for internal rotations, and a group additivity scheme is developed to predict à and E_a. The values predicted by group additivity are more accurate than structure-reactivity relationships currently used in the literature, which rely on representative à values and the Evans-Polanyi correlation. The structural factors that have the most pronounced effect on à and E_a are considered, and the presence of rings is shown to influence these values strongly.