Molecular symmetry - Symmetry operations, elements and point groups

5 important questions on Molecular symmetry - Symmetry operations, elements and point groups

What does the identity operator E do?

Does nothing to the molecule, every molecule has at least this operations.

What is n-fold rotation?

Symmetry operation if the molecule appears unchanged after rotation by 360/n. NH3 --> Rotation by 180 deg--> C2

What is the inversion operator?

An atom with coordinates x,y,z moves to -x,-y,-z. --> Centre of inversion.
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What is the improper rotation axis Sn?

Corresponding combination of an n-fold rotational axis and a perpendicular mirror plane. Example S2 axis: Rotation trough 180 deg followed by a reflection in the perpendicular plane, is equivalent to an inversion.

What does mirror plane imply?

Symmetry operation, reflection of an H2O molecule in either of the two planes: sigma1

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