Slate correlation diagram

Figure 6.21. Slate correlation diagram for ihe photochemical hydrogen abstraction, as calculated for Ihe system formaldehyde + methane (by permission from Devaquet el al., 1978).

If one s goal is merely to predict the number of spin-allowed transitions expected for a comfidex, a complete correlation diagram is not needed. It is only necessary to know the number of excited states having the same multiplicitv as the ground slate. 

A second selection rule stales that any Irataiiion for which S 0 is forbidden-. i.e.. in order to be allowed, a transition must involve no change in spin stale. Looking at the correlation diagram fora d configuration in an octahedral field (Fig. I I.3S), we note that the groiiiid slate has a multiplicily of 3 (5 = I) and that there ate three excited stales with this same multiplicily A3, and (bom Ihe / ). Thus we... 

The correlation diagram (Fig. 11.37d) is particularly interesting. The ground slate ( A, ) is the only state on the diagram with a multiplicity of 6. This means that for a d octahedral complex, all transitions are not only Laporte forbidden but also spin forbidden. Absorptions associated with doubly forbidden transitions are extremely weak, with extinction coefficients several hundred times smaller than those for singly forbidden transitions. It is understandable, then, that dilute solutions of Mn(II) are colorless and only with a substantial increase in concentration is the characteristic faint pink color of [MnfHiO) observable (Fig. 11.38b). 

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