Dear Sir,

as soon as you place an atom in a crystal there is no longer spherical symmetry as in case of an isolated atom. Therefore, the eigenfunctions of the electron are no longer described by the spherical harmonics but by the irreducible representations

of the actual point group. Since each crystal structure exhibits lower symmetry

than spherical symmetry, the degeneration of the electronic orbitals is lifted.

For example, the 5-fold degenerated d-orbital splits into a 2-fold degenerated Eg

level and a 3-fold T2g level in case that this atom is surrounded by ligands of

Oh symmetry (Oh = symmetry of an octaedron).

The labels A1g, A2g, B1g, B2g, T1g, T2g etc. just represent the irreducible representation of the particular point group, in the same way as the spherical

harmonics represent the irreducible representations of the spherical symmetry.

In case of your labels "1A, 1B, 2A, 2B", the left-hand numbers (usually superscripts) stand for spin multiplicity 2S+1. i.e. 2S+1 1 means S = 0, i.e., singlet, etc.

A and B representations are 1-fold degenerated states (with respect to

orbital degeneration)

For details, please refer to text books dealing with crystal field theory or

ligand field theory.

Sincerely, FM

Dear FM,

thank you so much for illuminating this topic with your relevant and much awaited reply,

kindest regards

N S Rawat