Bonds in molecules
What is the meaning of the bonds σ and π in molecules quantum mechanically?
Consider a molecular orbital in a diatomic molecule. The projection of the angular momentum of an electron in that orbital on the internuclear axis is designated by the quantum number ##\lambda##. In analogy with hydrogenic orbitals, the value of this quantum number is expressed with a letter according to
| \lambda | = 0 \Rightarrow \sigma \\
| \lambda | = 1 \Rightarrow \pi \\
| \lambda | = 2 \Rightarrow \delta \\
(note the absolute value, as the projection can be positive or negative).
For polyatomic molecules, a similar concept is applied in LCAO-MO theory where the molecular orbitals are built two atoms at a time.
An easy way to identify the value of ##| \lambda |## is to look along the bond and count the number of nodal planes. A ##\sigma## bond will look circular, a ##\pi## bond will be in the shape of a 8, similar to a p orbital in an atom.
Thank you very much. I like to know how to calculate angular momentum in molecular orbitals. Could you please give me a reference for that?
Landau Lifgarbagez, Quantum Mechanics, has a good discussion of the states of diatomic molecules apt for physicists.
Thank you. I will get it.
Read also: Enrico Fermi "Molecules, Crystals and Quantum Statistics".
Separate names with a comma.