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Molecular orbitals: H2

Bonding in hydrogen consists of a σ-bond. The corresponding anti-bonding orbital (σ*, pronounced "sigma star") is unoccupied, and can be represented by a molecular orbital constructed by the subtraction of the 1s wave function for one hydrogen atom from the other, followed by scaling to an appropriate size. The animation below shows this interaction of hydrogen 1s orbitals on two hydrogen atoms as they approach. The black dots represent the H nuclei. You will be able to see the electron density locating in the regions away from the internuclear axis, that is, the nuclei are becoming more exposed to each other.

The σ*-bond in dihydrogen (H2). This orbital is not occupied in H2.

The antibonding interaction of hydrogen 1s orbitals on two hydrogen atoms as they approach. This orbital is not occupied in H2.

Note the optical illusion where the orbital appears to recede. What is happening here is that you are seeing the orbital "isosurface" plotted for a constant value throughout. Antibonding orbitals are more diffuse thna the corresponding bonding orbitals and so the volume enclosed by the isosurface is less. To make this effect go away, what I really need to plot is a surface within which a constant percentage of the electron is located, but I haven't worked out how to make the ray tracer do that convincingly yet.

Note also that for a for a hydrogen atom the effective nuclear charge for its electron is 1. Howver in the H2 molecule the effective nuclear charge is a little higher and this has been factored into the animation. However, no attempt has been made to introduce the mixing of p functions into the animation.

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Document served: Tuesday 7th July, 2020