Temperature dependence of the reactions of small cobalt clusters with deuterium

Abstract

The kinetics of the reactions of cobalt clusters (Con' n = 9-21) with deuterium are studied over the temperature range 133-373 K. The measured rate constants for the dissociative addition of the first D2 molecule to COn' and their temperature dependences, are found to be strongly dependent on cluster size. CO IO _ 13 and C0 15 _ 17 are relatively reactive, with their reaction rates essentially independent of temperature, suggesting no significant reaction barrier for deuterium chemisorption. The reaction rate of C0 20 is nearly constant above 213 K, but increases at lower temperature. For C0 9 and CO I4 , the rate constants increase both at high and low temperatures. An increase at higher temperatures suggests the presence of activation barriers, while increases at low temperatures are interpreted as due to an increase in the initial trapping of D2 onto the clusters' surfaces. For COIS' CO I9 , and Co 21 , evidence for more than one isomer at low temperature is found. The experimental results are discussed in terms of cluster geometrical structure and the detailed reaction mechanism.140

Molecular adsorption of H2 on small cationic nickel clusters

“…Under the assumption that the reaction time is similar for all cluster sizes, the relative reactivity of Ni 5 Barriers to the formation of M n D 2 complexes have been found for cobalt and iron clusters of certain size. 13 It is possible that such barriers lead to a stabilization of a precursor state to dissociation in which the hydrogen is molecularly coordinated. However, such a state has never been directly observed experimentally.…”

Isomer selective infrared spectroscopy of neutral metal clusters

“…Geometric structure determination of metal clusters in the gas phase is difficult and for systems where isomers are present, the structure determination is even more challenging. For metal clusters, the coexistence of different isomeric structures has been experimentally revealed using mainly two methods: ͑i͒ investigation of the kinetics with reactant molecules, where bi-or multipleexponential reaction kinetics are signatures for the presence of isomers with different reactivities, [1][2][3][4][5] or ͑ii͒ ͑ion͒ mobility measurements, where isomers with different collision cross sections can be separated and detected via their different arrival time distributions. [6][7][8] Further evidence for metal cluster isomers is obtained from the measurements of magnetic moments, 9 from unimolecular photodissociation dynamics, 10 and from photoelectron spectroscopy.…”

Au‐induced decomposition of N2O

“…An upper bound of the pre-exponential factor A is given by the collision rate, kcoll. Lower A-factors are conceivable if the probability for N20 being trapped by a cluster is less than unity [33]. This would Inserting 0.4eV as an average value of &in and $ k B T ( T = 300 K ) as the kinetic energy of the gas molecules, one obtains center-of-mass energies of 0.13 eV for Au: and 0.084eV for Au:.…”