The key difference between Raman and FTIR: for a transition to be Raman active there must be a change in the polarizability of the molecule during the vibration. On the other hand, for an IR detectable transition, the molecule must undergo dipole moment change during vibration.
Uff - these are different physical principles, selection rules, wavelength/energy regions of the spectrum, (typical) spectral and spatial resolutions...
This chapter does some degree of comparison, in the context of biomedical applications.
“Raman Microscopy: Complement or Competitor?”,
Hugh J. Byrne, Ganesh D. Sockalingum and Nick Stone,
in ”Biomedical Applications of Synchrotron Infrared Microspectroscopy: A Practical Approach”, David Moss, (Editor), RSC Analytical Spectroscopy Monographs No. 11 (2011) ISBN: 978-0-85404-154-1
also
“A comparison of Raman, FTIR and ATR-FTIR micro spectroscopy for imaging human skin tissue sections”
S.M. Ali, F. Bonnier, H. Lambkin, K. Flynn, V. McDonagh, C. Healy, T.C. Lee, F.M. Lyng, H.J. Byrne,
Analytical Methods, 5, 2281-2291 (2013)
First of all the similarity:
Both techniques are used to monitor vibrational bands. But this fact is from my opinion the only similarity.
Multiple differences exist, see above. I want to name only one:
Raman “spectroscopy” is no spectroscopy at all. The scattered light is wavelength dependent analysed (shifted by the laser wavelength or wavenumber). Hence the concentration is proportional to the intensity whereas for all spectroscopic methods the concentration follows the Lambert-Beer law.
Note: The term “FT” only refers to the wavelength “selection” (in this case by an interferometer). Also FT-Raman is usual.
Whether you are using Raman spectroscopy or FTIR spectroscopy, both methods have advantages and limitations, but when combined, these two methods become a powerful tool when performing materials characterization.
FTIR spectroscopy is sensitive to hetero-nuclear functional group vibrations and polar bonds, especially OH stretching in water. Raman on the other hand is sensitive to homo-nuclear molecular bonds. For example, it can distinguish between C-C, C=C and C≡C bonds.
Raman spectroscopy requires little or no sample preparation while the FTIR method has constraints on sample thickness, uniformity and dilution to avoid saturation. The key advantage of FTIR is the difference in the two methods in dealing with interference. Fluorescence may interfere with the ability of taking Raman spectra, which would not be an issue with FTIR.
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