Question

Please compare infrared and Raman spectroscopy in the following perspectives:

1.Mostly used electromagnetic radiation;

2.Exemplary light source;

3.Responsive to the types of molecular bonds;

4.Interferences of air components, i.e. water and CO₂;

5.Usefulness in forensic analysis.  

Answer 1

1.Mostly used electromagnetic radiation;

Infrared Spectroscopy is the spectroscopy that deals with the infrared region of the electromagnetic spectrum.

Raman spectroscopy relies on inelastic scattering or Raman scattering, of monochromatic light, usually from the laser in the visible, near infrared or near ultraviolet range.

2.Exemplary light source;

Infrared Spectroscopy is the result of absorption of light by vibrating molecules as compared to Raman in which there is scattering of light by the vibrating molecules.

3.Responsive to the types of molecular bonds

For a transition to be Raman active there must be a change in the polarizability of the molecule during the vibration. This means that the electron cloud of the molecule must undergo positional change. On the other hand, for an IR detectable transition, the molecule must undergo dipole moment change during vibration. So, when a molecule is symmetrical, e.g. O₂, we cannot observe any IR absorption lines, since the molecule cannot change its dipole moment. It has been observed that molecules with a strong dipole moment are typically hard to polarize.

4.Interferences of air components, i.e. water and CO₂;

For both spectroscopy, the compound should free from air components, i.e. water and CO₂