Dissociation reactions of diatomic silver cations with small alkenes: experiment and theory

Reaction of ground-state Ag2+ (2Σg+, 4d20 σ(5s)1) with either ethene or propene leads to both simple ligand addition and loss of neutral Ag to form ligated Ag+. Rate constants for the dissociation of Ag2+ via association of both ethene and propene have been measured. Experimental and theoretical analysis suggests that loss of a neutral Ag atom occurs upon addition of either the second ethene or first propene ligand to the Ag2+ ion. The measured rate constants exhibit a negative temperature dependence and relatively high reaction efficiency suggesting that the dissociation reactions are exothermic. Electronic structure calculations were preformed using density functional theory (DFT) at the B3LYP level in order to generate potential transition state structures for the dissociation reactions. Phase space theory (PST) was used to model the experimental rate data. Good agreement was found between experiment, DFT calculations and PST results for both systems. In both reactions, the negative temperature dependence is due to two factors: The reactions are only mildly exothermic and the product density of states increases more slowly with energy than the reactant density of states. The second factor is due to an atom being one of the products. No evidence for tight transition states was found for either reaction.