Barycentre rule

Another way to view the barycentre rule is to consider first the bringing up to the metal of a spherical shell of negative charge which increases the energies of all five d orbitals equally. Then, in this notional picture, if the spherical shell of charge redistributes towards the apices of an octahedron, those orbitals directed towards those apices suffer a further repulsion and energy increase, while those directed in between, acquire a relative stability. 

Using this equation, it is possible to estimate that the energy level of Pr " (4/ ) will be located approximately 370 cm" or -12 below the barycentre of the level, while the will be 62 or 2220cm" above and the level -52 or 1850cm" below [16]. Erom Equation 1.24 it can further be concluded that the energy gap A between two adjacent levels with / = 7-1-1 is approximated by Tandy s interval rule (see also Eig. 1.3), given in Equation 1.25. 

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