Lecture 6 Vibrational spectra of complex molecules.

Lecture 6Lecture 6

Vibrational spectra of complex molecules

R-Q-P

Gas

Solid matrix

Sharp peaks!Sharp peaks!

Liquid acetone

Acetone in asolid matrix(*- admixtures)

Sharp peaks!Sharp peaks!

Fermi ResonanceFermi 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.

Fermi Resonance

Overtone

Fundamental bandFundamental band