Reaction of Mass-Selected, Thermalized V _nO _m⁺ Clusters with CCl₄

The kinetics of V _nO _m⁺ + CCl₄ ( n, m = 2, 5; 3, 6-8; 4, 9-11; 5, 12-13) have been measured under thermal conditions using a selected-ion flow tube equipped with a laser vaporization ion source. All reactions proceed at approximately the capture rate limit, yielding three dominant categories of products: CCl₃⁺ + V _nO _mCl (i.e., chloride transfer), COCl₂ (phosgene) formation, and CO₂ formation. Both CO₂ and COCl₂ are products of CCl₄ reaction on a bulk vanadium oxide surface, while chloride (or chlorine) transfer is not observed. The product branching fraction of CCl₃⁺ approaches 100% for small (V₂) reactants and generally decreases with increasing cluster size down to <5% for V₅O₁₃. The fraction of chloride transfer is correlated to the fraction of terminal oxygen atoms in the V _nO _m⁺ reactant. As cluster size increases, phosgene replaces chloride transfer as the dominant product channel. The channel producing CO₂ is observed only for highly oxygenated clusters, V₃O₈⁺, V₄O₁₁⁺, and V₅O₁₃⁺, and appears to require a superoxide O₂ in the reactant structure; the mechanism is likely distinct from that producing CO₂ on bulk V₂O₅. Increasing the temperature of the system from 300 to 500 K increases the observed fraction of CCl₃⁺ at the expense of all other product channels. Likely mechanisms, informed by density functional calculations, are discussed.