The extended alkali model

However, there is one important difference in this new situation the ionisation limits now correspond to highly excited states of the core. If these are fairly stable (as in fig. 2.9) then long series can be built on them. If, on the other hand, the parent ion states decay very rapidly, then Rydberg excitation can be quenched, especially for the highest Rydberg states which would have long natural lifetimes in the absence of core deexcitation. 

To demonstrate how useful the alkali model is for d subshell excitation in Zn, Cd and Hg, consider the effective quantum numbers n listed in table 2.2 for np and nf orbitals. The behaviour of these numbers is closely similar to that for alkali spectra, with the most hydrogenic states (near integral n ) being those of greatest , while the n values indicate that the outermost np electron, in its lowest available state, occurs at a binding energy (referred to a core-excited threshold) intermediate between the values for n = 1 and n = 2 of H. 

The lowest available state in this case is obtained by counting which 

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In section 2.12 which dealt with the extended alkali model, it was pointed out that inner-shell excitation of an atom with a closed outer shell results... 

These spectra have already been used in section 2.12 as examples of the extended alkali model. They correspond to the excitation scheme d10 2 1So — d9 2np,nf(J = 1), where 2 are the valence electrons. Double excitations have also been investigated, especially in Zn [344] and are very significantly enhanced as they approach an inner-shell excited transition. This shows that final state mixing is the dominant mechanism for double excitation. 

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