Difference Between IR and Raman Spectra

The differences between Raman and IR spectroscopy: The fundamental principles that govern each method - the Raman effect is weak, resulting from an inelastic raman scattering process that occurs when light interacts with molecules; IR spectroscopy is a stronger technique that relies on absorption of light by molecules.

1. Why Raman spectra is more useful than IR spectra?
2. What is the difference between Rayleigh and Raman scattering?
3. What is the difference between IR and FTIR?
4. What are the selection rules for Raman and IR spectroscopy?
5. Which is not an IR vibrational mode?
6. What is the selection rule of Raman spectra?
7. What are the three types of scattering?
8. Which type of scattering is the strongest?
9. Why is Raman scattering weak?
10. Why KBr is used in FTIR?
11. Which lamp is used in IR?
12. What does FTIR detect?

Why Raman spectra is more useful than IR spectra?

 An important advantage of Raman spectra over infrared lies in the fact that water does not cause interference, indeed, Raman spectra can be obtained from aqueous solutions. 12.  Water can be used as a solvent.  Very suitable for biological samples in native state (because water can be used as solvent).

What is the difference between Rayleigh and Raman scattering?

1 Answer. Raman scattering is inelastic scattering from molecules. The photon interacts with the molecule and changes the molecules vibrational, rotational or electron energy. Rayleigh scattering is in the main elastic scattering from small particles whose size is less than that of the wavelength of the photon.

What is the difference between IR and FTIR?

FTIR spectrometers have several prominent advantages: (1) The signal-to-noise ratio of spectrum is significantly higher than the previous generation infrared spectrometers. (2) The accuracy of wavenumber is high. ... Due to these advantages, FTIR Spectrometers have replaced dispersive IR spectrometers.

What are the selection rules for Raman and IR spectroscopy?

Raman: Scattering of visible light with loss (or gain) of frequency corresponding to vibrational quanta. IR Selection Rule: For any IR absorption, the vibrational excitation must change the dipole moment of the molecule in order for radiation absorption to occur.

Which is not an IR vibrational mode?

Molecular Vibrations

Diatomic molecules are observed in the Raman spectra but not in the IR spectra. ... The normal modes of vibration are: asymmetric, symmetric, wagging, twisting, scissoring, and rocking for polyatomic molecules.

What is the selection rule of Raman spectra?

For vibrational Raman spectroscopy, the gross selection rule is that the polarizability of the molecule should change as it vibrates. The specific selec- tion rule for vibrational Raman spectroscopy is ∆v = ±1, where the ∆v = 1 corresponds to Stokes lines and the ∆v = −1 corresponds to Anti-Stokes lines.

What are the three types of scattering?

There are three main types of scattering that impact incoming solar radiation:

• Rayleigh Scatter.
• Mie Scatter.
• Non-Selective Scatter.

Which type of scattering is the strongest?

Another finding is that forward scattering is stronger than backward scattering, because the relative phase differences of contributions from different scattering locations on the particles become smaller.

Why is Raman scattering weak?

This occurs because only molecules that are vibrationally excited prior to irradiation can give rise to the anti-Stokes line. Hence, in Raman spectroscopy, only the more intense Stokes line is normally measured - Raman scattering is a relatively weak process. The number of photons Raman scattered is quite small.

Why KBr is used in FTIR?

Potassium bromide (KBr, spectroscopic grade) is typically used as the window material because it is transparent in the IR, between 4000–400 cm-1. Alternatively, samples can be contained within a KBr matrix and pressed to form a pellet that is then analysed.

Which lamp is used in IR?

NIR lamp (filament temperature: 3,000 K) Short-wave infrared lamp (filament temperature: 2,300 K) Medium-wave infrared lamp (filament temperature: 900 K) Fast medium-wave infrared lamp (filament temperature: 1,600 K)

What does FTIR detect?

Fourier Transform-Infrared Spectroscopy (FTIR) is an analytical technique used to identify organic (and in some cases inorganic) materials. This technique measures the absorption of infrared radiation by the sample material versus wavelength. The infrared absorption bands identify molecular components and structures.