Substrates diatomic molecules

The binuclear [2Fe]n cluster is believed to be the substrate binding and activation site. It has a most unusual structure with the two iron atoms (Fel and Fe2) bridged by two thiolates of a 1,3-propanedithiol group and a diatomic molecule, probably a CO (Peters et al. 1999 Nicolet et al. 2000). 

If we wish to understand the conditions under which a diatomic molecule such as H2, N2, or CO dissociates on a surface, we need to take two orbitals of the molecule into account - the highest occupied and the lowest unoccupied molecular orbital (the HOMO and LUMO of the so-called frontier orbital concept). Let us take a simple case to start with the molecule A2 with occupied bonding level a and unoccupied antibonding level a. We use jellium as the substrate metal and discuss the chemisorption of A2 in the resonant level model. What happens is that the two levels broaden due to the rather weak interaction with the free electron cloud of the metal. 

The mean amplitude of molecular vibration can be calculated from the vibrational frequency [74] and vice versa. For the frustrated rotation of an upright diatomic molecule adsorbed on heavy substrate atoms and a vibrational mode which is doubly degenerate, the mean square amplitude at equilibrium temperature Ts is given by [68]... 

In the case of non-dissociative adsorption of a diatomic molecule, two items of geometrical information can be extracted from the ARUPS data, the first being the bond angle between the molecular axis and the surface. The important assumption here is that certain major features of the spectrum should be determined by the adsorbate alone and be independent of the substrate, particularly if the initial states are not involved in the bond to the surface. This is the case for the 4a and Irt states of CO on Ni(lOO), for example. 

The magnitude of AZ/a s can tell us whether a diatomic molecule remains intact upon adsorption or dissociates into its constituent atoms. For adsorption as a diatomic molecule, AH. ds is defined as the energy needed to break the bond between the substrate (M) and the adsorbed molecule (X2), MX2 ... 

New aspects may evolve in future experiments from studies of these diatomic molecules on various high-quality substrates. Investigations on boron nitride surfaces have just been started. Here, one of the most interesting questions is How do the different electrical properties of this substrate compared to those of graphite influence the behavior of the adsorbed film The... 

Diatomic Molecules as Possible Diagnostic Reagents and the Use of Correlation Diagrams. Since the primary reactions of polyvalent atoms are expected to form reactive intermediates, the most general approach to characterizing these primary reactions is to pick substrates whose reactions are most likely to convey information about the electronic states of the reacting atom and the geometry of its attack on the substrate. 

In general terms, it appears that transition states for dissociative adsorption are very similar. For a given substrate geometry, it is essentially independent of the molecule and transition metal in question [218]. This was shown by Norskov et al. [57] by linear plots (Bronsted Polyani plots) of calculated activation energies for diatomic molecules versus calculated adsorption energies of the dissociated atoms. The plot for stepped surfaces showed activation energies below those for close-packed surfaces [333], which is mainly due to a geometric effect. 

Fig. 12. One-dimensional simulations of energy-loss spectra for He scattering from diatomic molecules adsorbed on metal substrates. NjWj , OCPt, , OCNigo (full lines) and from the pure metals Wg , Pt,(, Ni, (dashed lines), calculated for the collision energy = 0.5eV, target temperature r = 77K and detector resolution 4, = 5meV. The intensities have been normalized so that their maxima equal unity.

FIGURE 6.1 Schematic energy profile for the adsorption of some diatomic molecule Aj on some substrate as a function of a specific reaction coordinate, which could be the distance between the substrate surface and the center of mass of the molecule. 

In summary, the interaction of ozone with molecules of substrate (reaction 1) is the limited step of the process of ozone oxidation of PVA as well as for mono- and diatomic alcohols. 

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