Temperature effects in transition metal ion and cluster ion reactions

While reactions on the surface of bulk metal proceed in general under well- defined and experimentally easily measurable temperature and other conditio ns, this is usually not the case for reactions of metal atoms or clusters a nd their ions in high vacuum. A collision complex of the metal cluster with a polyatomic molecule (e.g., benzene) may be transiently stabilized by red istribution of the interaction energy, IVR. This energy redistribution resu lts in heating of the collision complex to internal temperatures, which can be estimated to be often very high, but the data for its exact determinati on are usually not available. Semiquantitatively, the heat capacity of the complex will increase with the cluster size, and the temperature rise upon complex formation will correspondingly decrease. Such size-dependent heatin g effects are readily observable in FT-ICR studies of anionic and cationic cluster reactions, and when interpreting the data or trying to draw from it conclusions for bulk condensed phase reactions, they have to be taken into consideration. Conversely, the effect of such temperature rise in mass spe ctrometric studies can be decreased or eliminated, and the reactions of tru ly cold clusters can be investigated by "soft landing" the reactive molecul e on a solvated cluster and exchanging it for inert ligands, e.g., argon at oms.