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, (A) over tilde, 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 (A) over tilde 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 (A) over tilde values and the Evans-Polanyi correlation. The structural factors that have the most pronounced effect on (A) over tilde and E-a are considered, and the presence of rings is shown to influence these values strongly.