What is the definition of Raman spectroscopy? How to explain in brief about antistoke line and Stoke line and Rayleigh?
$\begingroup$
$\endgroup$
Add a comment
|
1 Answer
$\begingroup$
$\endgroup$
Raman spectroscopy is an instance of inelastic scattering of light by molecules in the lattice.
Suppose the lattice was in some particular vibrational and rotational state. When light is incident on the material, the molecules get excited to a high energy virtual state, which is short lived. If the molecule jumps back to its initial state, the photon is released without any change in energy, this corresponds to the elastic Rayleigh Scattering.
If the molecule moves to a state that is higher in energy compared to its previous state, the photon loses some of its energy in this phonon excitation, hence the released phonon will have lower energy, this shift corresponds to the Stoke line. In contrast, if the molecule moves to a state that is lower in energy compared to its initial state, it has de-excited/absorbed a phonon and has gained energy, this shift corresponds to the Anti-Stokes line. These are quite well explained in the Wikipedia article.
Typically the phonons created correspond to transitions to the optical branches at the gamma point. Since the momentum of photons are negligible compared to the extent of the Brillouin zone, these transitions are nearly vertical in the phonon dispersion plots.
