Vibrational spectra of complex molecules

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Lecture 6

• Vibrational spectra of complex molecules

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R-Q-P
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Gas
Solid matrix
Sharp peaks!
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Liquid acetone
Acetone in a solid matrix (- admixtures)
Sharp peaks!
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Fermi Resonance
Overtone weak (forbiden)
Resonance line much stronger, shifted, and
allowed
Two conditions must be satisfied for the
occurrence of Fermi Resonance (1) the two
vibrational states of a molecule transform
according to the same irreducible representation
of the molecular point group. (2) The energies of
the transitions (accidentally) have almost the
same energy.
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Overtone
Fundamental band
Fermi Resonance
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