Three level systems, atomic species

Atomic Systems. Many atomic species may be modeled as three-level systems. Figure 2 illustrates the energy level diagram for sodium. Other alkali and alkaline metals behave in a similar manner. 

Lack of understanding of the above mentioned issues has led to intense study of not only what is happening on the atomic level, but also the design of new systems that have both higher selectivity and rates of conversion. Three main systems were studied thus far silver-alumina type catalysts, silver-modified manganese species, and silver-modified ceria (Ce02) systems. 

Two wider ranging, more systematic investigations of conformational dependence have since been performed to establish whether the conformational sensitivity noted in the above PECD smdies may generally provide a means for identifying and distinguishing gas-phase structure of suitable chiral species. The B-spline method has been applied to the model system (l/f,2f )-l,2-dibromo-l,2-dichloro-l,2-difluoroethane [60]. Rotation around the C C bond creates three stable conformational possibilities for this molecule to adopt. The results for both core and valence shell ionizations reaffirm an earlier conclusion a and p are almost unaffected by the rotational conformation adopted, whereas the PECD varies significantly. Eor the C Ij ionization to show any sensitivity at aU to the relative disposition of the halogen atoms further reinforces the point made previously in connection with the core level PECD phenomenon. 

The molecular orbitals of the allyl system are formed by the overlap of three atomic p orbitals. Because there is an odd number of atomic orbitals, one of the molecular orbitals is a nonbonding orbital, whose energy is comparable to that of the isolated p orbitals from which it was derived. Note that if there were degenerate molecular orbitals in the allyl system, the electronic configurations of various allyl species would be different. For example, if P2 3 for the allyl system had identical energy levels, the allyl anion would have two unpaired electrons. 

---