Temperature Effects in Transition Metal Ion and Cluster Ion Reactions

Abstract

While reactions on the surface of bulk metal proceed in general under well-defined and experimentally easily measurable temperature and other conditions, this is usually not the case for reactions of metal atoms or clusters and their ions in high vacuum. A collision complex of the metal cluster with a polyatomic molecule (e.g., benzene) may be transiently stabilized by redistribution of the interaction energy, IVR. This energy redistribution results in heating of the collision complex to internal temperatures, which can be estimated to be often very high, but the data for its exact determination 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 heating 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 spectrometric studies can be decreased or eliminated, and the reactions of truly cold clusters can be investigated by “soft landing” the reactive molecule on a solvated cluster and exchanging it for inert ligands, e.g., argon atoms.

Reaction of niobium and tantalum neutral clusters with low pressure, unsaturated hydrocarbons in a pickup cell: From dehydrogenation to Met-Car formation

“…If roughly ten collisions ͑10-500 ns͒ are required to cool and stabilize the collision complex efficiently, formation of the metastable complex Nb n C 6 H 6 * by IVR must also happen in the flow tube experiment, otherwise no direct association product would be observed. On the basis of the above observations and in agreement with the results for the cationic cluster system, 25 we conclude that the metastable association complex Nb n C 6 H 6 * is formed in both the pickup and flow tube reactor cells.…”

“…Based on the high interaction energy ͑2-3 eV͒ 26 between charged metal atom/cluster and organic ligands ͑e.g., C 6 H 6 ͒, a long lived collision complex formation and an effective temperature increase following intracluster vibrational energy redistribution of the interaction energy has been proposed by Bondybey and Beyer. 25 This mechanism was offered to explain their FT-ICR findings of dehydrogenation products and is further supported by a ligand exchange experiment in which less dehydrogenation is usually observed if the cluster is solvated by inert gas atoms prior to reaction. The interaction energy between neutral clusters and unsaturated hydrocarbons is relatively small, ca.…”

Formation, Structure, and Reactivity of Gaseous Ni2O2+

“…Attenuation of reactivity associated with the transition from mononuclear to dinuclear transition‐metal oxides is a general trend also observed for manganese11 and iron 12,13. The lower charge densities of the cluster ions and their higher degrees of valence saturation are likely reasons for the more moderate reactivities 37. As stated initially, exactly these properties add to their attractiveness as model compounds for real catalysts in the condensed phase.…”

Structural Properties of Gas Phase Molybdenum Sulfide Clusters [Mo3S13]2–, [HMo3S13]−, and [H3Mo3S13]+ as Model Systems of a Promising Hydrogen Evolution Catalyst

“…We use Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) as an excellent tool for the investigation of ion–molecule reactions, 36−39 including catalytic cycles, 40−45 as well as for characterization of nanoclusters in the gas phase. 46−49 Additionally, the results of the experiments are interpreted with the help of quantum chemical calculations.…”