What is the Difference Between Fermi Resonance and Overtones in IR Spectra?
🆚 Go to Comparative Table 🆚Fermi resonance and overtones are both phenomena observed in infrared (IR) spectra, but they have distinct differences:
- Fermi Resonance:
- It is the shifting of the energies and intensities of absorption bands in an IR or Raman spectrum.
- It occurs due to quantum-mechanical wavefunction mixing, as explained by Italian physicist Enrico Fermi.
- It requires that the two vibrational modes have the same irreducible representation and that their energies are nearly coincident.
- Fermi resonance leads to two effects: the high-energy mode shifts to higher energy, and the low-energy mode shifts to still lower energy. The weaker mode gains intensity (becomes more allowed), and the more intense band decreases in intensity.
- Overtones:
- Overtones are spectral bands that occur in a vibrational spectrum upon the IR spectra.
- Overtones are the result of a transition with Δv > 1 from the ground state.
- Overtones generally have lower intensities than the fundamental transitions.
- Overtones decrease in probability as the number of quanta (Δv) increases.
In summary, Fermi resonance is a quantum-mechanical phenomenon that leads to shifts in energies and intensities of absorption bands, while overtones are spectral bands resulting from vibrational transitions with higher energies than the fundamental transitions.
On this pageWhat is the Difference Between Fermi Resonance and Overtones in IR Spectra? Comparative Table: Fermi Resonance vs Overtones in IR Spectra
Comparative Table: Fermi Resonance vs Overtones in IR Spectra
The main differences between Fermi resonance and overtones in IR spectra are as follows:
Fermi Resonance | Overtones |
---|---|
Fermi resonance results in the shifting of the energies and intensities of adsorption bands in an IR or Raman spectrum. | Overtones are spectral bands that occur in a vibrational spectrum upon the IR or Raman spectra. |
It is a consequence of the quantum mechanical wavefunction mixing. | Overtones generally have lower intensities than the fundamental vibrational frequencies. |
Named after Italian physicist Enrico Fermi. | Overtones can be used to help explain and assign peaks in vibrational spectra that do not correspond to the fundamental vibrational frequencies. |
Fermi resonance helps explain and assign peaks within IR and Raman spectra that may not otherwise be accounted for, while overtones are used to explain spectral bands in vibrational spectra.
Read more:
- IR vs Raman Spectra
- FTIR vs Raman Spectroscopy
- Hyperconjugation vs Resonance
- Isomers vs Resonance
- Emission vs Absorption Spectra
- IR vs UV vs Visible Spectroscopy
- Conjugation vs Resonance
- Resonance vs Natural Frequency
- Fermi Energy vs Fermi Level
- Fermi Energy vs Fermi Level
- Delocalization vs Resonance
- Atomic Spectroscopy vs Molecular Spectroscopy
- Absorption Spectrum vs Emission Spectrum
- Flame Emission Spectroscopy vs Atomic Absorption Spectroscopy
- Resonance vs Tautomerism
- Inductive Effect vs Resonance Effect
- Prism Spectra vs Grating Spectra
- Spectroscopy vs Spectrometry
- Rotational vs Vibrational Spectroscopy