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Sunday, February 2, 2020

What is Laporte Selection rule?

Laporte Selection Rule is given by Otto Laporte a German American Physicist

According to Laporte selection rule only allowed transitions are those occurring with a change in parity (flip in the sign of one spatial coordinate.) OR During an electronic transition the azimuthal quantum number can change only by ± 1 (Δ l = ±1) The Laporte selection rule reflects the fact that for light to interact with a molecule and be absorbed, there should be a change in dipole moment.

Practical meaning of the Laporte rule:

Laporte allowed transitions: are those which occur between gerade to ungerade or ungerade to gerade orbitals.

Laporte forbidden transitions: are those which occur between gerade to gerade or ungerade to ungerade orbitals.

Gerade = symmetric with respect to centre of inversion i.e. atomic or molecular orbital with center of symmetry or number of nodal plane = 0, 2, 4 (even number)

Ungerade = anti symmetric with respect to centre of inversion i.e. atomic or molecular orbital without center of symmetry or number of nodal plane = 1, 3, 5, (odd numbers)

Important Note:

This rule affects Octahedral and Square planar complexes as they have center of symmetry. Tetrahedral complexes do not have center of symmetry therefore this rule does not apply