What is the Difference Between IR and Raman Spectra?
🆚 Go to Comparative Table 🆚The main differences between IR and Raman spectra lie in the mechanism of interaction with the sample, the information they provide, and the experimental setup:
- Mechanism:
- IR spectroscopy depends on the change in the dipole moment of a molecule.
- Raman spectroscopy depends on the change in polarizability of a molecule.
- Information:
- IR spectroscopy measures the absolute frequencies at which a sample absorbs radiation.
- Raman spectroscopy measures the relative frequencies at which a sample scatters radiation.
- IR spectroscopy is sensitive to hetero-nuclear functional group vibrations and polar bonds, especially OH stretching in water.
- Raman spectroscopy is sensitive to homo-nuclear molecular bonds, such as C-C, C=C, and C≡C.
- IR spectroscopy provides a "fingerprint region" of the spectrum where intramolecular vibrations are observed.
- Raman spectroscopy yields information about intra- and intermolecular vibrations.
- Experimental Setup:
- IR spectrometers typically employ a black body radiator.
- Raman spectrometers utilize a laser as the source, typically visible or near-IR laser.
- Raman spectra result from the scattering of light by vibrating molecules.
- IR spectra result from light absorption by vibrating molecules.
- In Raman spectroscopy, scattered light is observed at right angles to the direction of the incident beam.
Both techniques offer molecular information and can be used with microscopic techniques, but the choice between them depends on the nature of the application and the desired information.
On this pageWhat is the Difference Between IR and Raman Spectra? Comparative Table: IR vs Raman Spectra
Comparative Table: IR vs Raman Spectra
Here is a table comparing the differences between IR and Raman spectra:
Feature | IR Spectroscopy | Raman Spectroscopy |
---|---|---|
Vibrational Modes | Asymmetric vibrations are strong | Symmetric vibrations are strong |
Bond Substitution | Strong for asymmetrically substituted bonds | Strong for symmetrically substituted bonds |
Vibrational Symmetry | Difficult to determine | Can determine vibrational symmetry |
Interaction Mechanism | Bands arise from the interaction of light and an oscillating dipole moment of a molecule | Bands arise from an oscillating induced-dipole due to the interaction between light waves and a molecule |
Molecular Symmetry | Asymmetric molecules demonstrate IR and Raman spectra bands at similar frequencies, but with different intensities | Not applicable |
Both IR and Raman spectroscopy are complementary techniques for analyzing the vibrational modes of molecules, and they provide information about the molecular structure and bonding. The main differences between the two techniques lie in the vibrational modes they emphasize and the interaction mechanisms involved.
Read more:
- FTIR vs Raman Spectroscopy
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- Rayleigh vs Raman Scattering
- Fermi Resonance vs Overtones in IR Spectra
- Emission vs Absorption Spectra
- Spectroscopy vs Spectrometry
- Rotational vs Vibrational Spectroscopy
- Prism Spectra vs Grating Spectra
- Atomic Absorption Spectroscopy vs UV Visible Spectroscopy
- Absorption Spectrum vs Emission Spectrum
- Atomic Spectroscopy vs Molecular Spectroscopy
- Spectrometer vs Spectrophotometer
- Colorimetry vs Spectrophotometry
- Colorimeter vs Spectrophotometer
- Flame Emission Spectroscopy vs Atomic Absorption Spectroscopy
- Spectrophotometer vs Spectrofluorometer
- Photometry vs Spectrophotometry
- Hydrogen vs Helium Emission Spectra
- Action Spectrum vs Absorption Spectrum