Raman!

photon79

Hi , I heard that the speciality of Raman spectroscopy is "Single molecule identification", it'd be really great if somebody can tell me HOW! because its surely going to be a question in my exam!!
Thanks in advance.

inha

Raman scattering excites low energy vibrational and rotational modes which are very target specific. I guess that's how the molecules are indentified. Someone else can probably give you more info because I only have limited knowledge on X-ray Raman scattering and it seems you're asking about Raman scattering around the laser region.

photon79

Thnks inha,,you are right, I was looking in laser excitations.

Claude Bile

What do you mean by single-molecule identification. Do you mean that a sample can be identified with only a single-molecule present?

Claude.

photon79

That is what I want to know,i think it is not same as you said but it is connected with the Surface enhanced Raman spectroscopy(I think).
It might be identifying a given unknown sample using info about its symmetry !!!!!!

Gokul43201

Yes, SMD (single molecule detection) is done using SERS. The reason you need SERS is scattering cross-section. With regular Raman scattering, the cross-section is typically of order 10^{-30] cm^2. With SERS, you get as much as about 10^{-15} cm^2 (or thereabouts).

photon79

Ok , Thanks Gokul!
I dodn't get what scattering cross section has to do with molecule identification, more info please! (or any web site?)

inha

With a small scattering cross section the experiment would take ages or fail totally as the relevant information would get buried into the background.

Claude Bile

Exactly, larger scattering cross-section = more scattered photons = greater signal-to-noise ratio.

Claude.