Multiatom clusters

Sachtler and coworkers showed evidence of CO adsorption on monoatomic Pt with a CO vibrational frequency at 2123cm Hn H-MOR zeolite [142]. This band is shifted to significantly higher frequencies than the -2070 cm band that is typically observed for CO on multiatomic clusters. They proposed that these electron-... 

The solid-phase diffusion of monoatomic metal (or its oxide) particles to give multiatomic cluster particles. It is assumed that diffusion processes in the solid phase are activated. The rate of diffusion = DnC = C Di where C = Cla is the current amount of reaction centers per one cell of the a size, N is the size of A-atomic cluster, Di = Doexp[- aE/( T)] is the diffusion coefficient for a monoatomic particle, EaX) and Do = vexp(A57/ ) are the varying parameters, the energy of activation, and the entropy factor ((v 10 sec" ). Such a model assumes that the coexistence of two or more separate particles in one cell is not possible because they immediately form a single cluster. In the isotropic medium the diffusing particle with a corresponding probability can move in one of the 26 directions. 

Atoms of metals are more interesting tiian hydrogen atoms, because they can form not only dimers Ag2, but also particles with larger number of atoms. What are the electric properties of these particles on surfaces of solids The answer to this question can be most easily obtained by using a semiconductor sensor which plays simultaneously the role of a sorbent target and is used as a detector of silver adatoms. The initial concentration of silver adatoms must be sufficiently small, so that growth of multiatomic aggregates of silver particles (clusters) could be traced by variation of an electric conductivity in time (after atomic beam was terminated), provided the assumption of small electric activity of clusters on a semiconductor surface [42] compared to that of atomic particles is true. 

Under the high density after the impact, several O2 and N2 molecules can interact simultaneously. While the high density conditions prevail, many reactions can occur through different mechanisms the four-center N2 + O2 —> 2NO reaction and the Zeldovich - type atom-diatom reactions, O -t- N2 —> NO + N and N -t- O2 — NO -t- O, just as in the case of a cluster containing a single N2/O2 pair, and also by a new mechanism, a multicenter one, where more than four atoms interact simultaneously. A snapshot of a multiatom configuration is shown in Fig. 20. 

Thus we see that the results of Table XVI can be reconciled with the geometric effect of multiatom sites associated with crystallite edges. For FE > 0.5, both the geometric and the cluster-like electronic effects lead to a rapid decrease in TOF to zero. 

Taking into account the cluster dissociation in the reaction [M ] [M il + M with formation of multiatomic particles that move to the neighbor cells. The rate of process = UnCn = C)v A/exp[- aA/( 7)] depends on the cluster size N and diminishes with its growth. Cm is the current concentration of cluster particles of the N size, and Eon and koN are the energy of activation for the A-cluster and preexponential factor ("lO sec" ), respectively. The energy of activation can vary and... 

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