Representations, characters and normal-mode reduction
Matrices representing symmetry operations on a chosen basis must reproduce group composition.
Key knowledge
Matrices representing symmetry operations on a chosen basis must reproduce group composition. Their traces are characters, which are unchanged by basis similarity transformations. Character orthogonality gives the multiplicity of each irreducible representation in a reducible representation. Molecular displacement representations can then be separated into translations, rotations and vibrations.
Values and equations
aμ = (1/|G|) ΣR χred(R) χμ(R)*
- aμ
- multiplicity of irreducible representation μ 1
- |G|
- number of group operations 1
- R
- operation summed over G group element
- χred(R),χμ(R)
- characters of reducible and irreducible representations 1
- *
- complex conjugation operation
Conditions and scope
- Use all group operations or conjugacy classes with the correct class sizes and complex conjugation.
- For a nonlinear free molecule subtract three translations and three rotations; linear molecules have two independent rotations.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Read matrix action, trace/basis invariance, reduction formula and NH3 Cartesian-mode example on pp.3–8; no complete group-theory theorem proof or universal frequency-count claim supplied.
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Entry details
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- uni-chem-character-reduction
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- core.1
- Structured reference record
- University core expansion