Reaction of Mass-Selected, Thermalized VnOm+ Clusters with CCl4

The kinetics of VnOm+ + 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+ + VnOmCl (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 VnOm+ 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.