Question

What is the diffrrent between ir and raman spectroscopy?

Answer 1

The main difference between the two techniques lies in the nature of the molecular transitions taking place. 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.