Reaction of Mass-Selected, Thermalized V O Clusters with CCl.

The kinetics of V O + CCl ( 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: CCl + V O Cl (i.e., chloride transfer), COCl (phosgene) formation, and CO formation. Both CO and COCl are products of CCl reaction on a bulk vanadium oxide surface, while chloride (or chlorine) transfer is not observed. The product branching fraction of CCl approaches 100% for small (V) reactants and generally decreases with increasing cluster size down to <5% for VO. The fraction of chloride transfer is correlated to the fraction of terminal oxygen atoms in the V O reactant. As cluster size increases, phosgene replaces chloride transfer as the dominant product channel. The channel producing CO is observed only for highly oxygenated clusters, VO, VO, and VO, and appears to require a superoxide O in the reactant structure; the mechanism is likely distinct from that producing CO on bulk VO. Increasing the temperature of the system from 300 to 500 K increases the observed fraction of CCl at the expense of all other product channels. Likely mechanisms, informed by density functional calculations, are discussed.