Electronic states of diatomic molecules

Concepts and nomenclature of electronic states

We assume a nonrotating fixed nuclear frame in the BO approximately with is average value of

reflection

inversion

Rotation by

Molecular symmetry

Doublet splitting

Electronic angular momenta

Electronic angular moenta l and s

In the united a form picture a molecule with and has a nucleus of charge , is constant in the spherically symmetrical potential. Pulling now the two nuclei apart to the equilibrium distance of the molecule produces an axially symmetrical electric field and experiences a torque

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which leads to a precession around the nuclear axis and only the projection is constant.

Approximation of separated atoms

Approximation of the united atom

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Example Li

2

Example BH

Correlation diagram for a homonuclear diatomic molecule

In the molecule orbital theory one works out for each electron orbital the according to

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and gets the total electronic energy as