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.