Reactivity of Fe_n, Co_n, and Cu_n Clusters with O₂ and D₂ Studied at Single-Collision Conditions

Abstract

This paper describes a method to study the reactivity of neutral clusters at single-collision-like conditions, which enables the determination of absolute numbers for the reaction probability (S) in a collision. A beam of clusters is produced in a laser vaporization source and skimmed and passes a cell with reactive gas, in which the clusters experience one or a few collisions with the gas molecules. The reaction products are detected with laser ionization and mass spectrometry. The depletion of pure clusters and the appearance of products are evaluated with a statistical model providing S for the first, second, etc., molecule adsorbed. The O2 and D2 reactivity of Fe n , Co n , and Cu n has been investigated for clusters in the approximate size range 10−60 atoms. The oxidation of transition metal clusters, here exemplified by Co n and Fe n , shows a simple S vs n dependence, where S increases almost monotonically as n increases from 10 to 20, while for larger n, S remains high and almost constant; S ≈ 0.7 for both Fe n and Co n . The low O2 reactivity measured for the small transition metal clusters may be an effect of the products having a short lifetime due to the high exothermicity of the oxidation reaction. For copper clusters there are repeated minima in the O2 reactivity appearing at cluster sizes that are known to have high IP and closed electronic shells. Co n is much less reactive toward D2 than O2, and S for D2 on Co n exhibits large size to size fluctuations. Cu n and small Fe n appear unreactive (detection limit S ≈ 0.02) toward D2, whereas the larger Fe n (n ≥ 23) react with a low probability.

Stability of Aluminum-Doped Copper Cluster Cations and Their Reactivity toward NO and O2

“…The total reaction cross section tends to increase with the number of Cu atoms and also exhibits a clear even−odd alternation in n ≥ 10. For all the clusters studied, the measured total reaction cross sections (<10 Å 2 ) are considerably smaller than the Langevin cross section (σ LGS = 47.4 Å 2 ) estimated using α(O 2 ) = 1.58 Å 3 (ref 27) and the hard-sphere cross sections (σ HS = 70−112 Å 2 ) 19 for the size range studied here. Cu 15 Al + shows the largest reaction cross section (8.3 Å 2 ) whereas Cu 5 Al + and Cu 6 Al + are unreactive at this collision energy.…”

N 2 on tungsten clusters: Molecular and dissociative adsorption

“…As in our previous studies, 9 we evaluated the reaction probability by fitting a pseudo-first-order kinetic model to the relative abundance of both bare and reacted clusters as a function of average number of cluster-molecule collisions in the reaction cell. The fitting parameters are the individual reaction probabilities, S 1 , S 2 , and S 3 for the successive adsorption of the first, second, and third N 2 molecule.…”

The structural and electronic properties of small osmium clusters (2–14): A density functional theory study

“…[1] These small clusters have unique reactivity, magnetic and catalytic properties that change as the number of atoms increases. [2,3,4] When it comes to magnetism, small magnetic clusters tend to have much larger magnetic moments than their bulk state. [5,6,7] In particular, group VIII metal clusters, small Fe and Ru clusters, have been inten-sively studied due to their strong magnetism and reactivity.…”