Raman Effect and Fluorescence: Understanding the Differences and Mechanisms

[ananthu]

Homework Statement

I understand that in the fluorescence, the incident photon is absorbed by the molecule, and the molecule while returning to its original ground level releases lesser energy. Similarly, in Raman effect also a photon is incident on a liquid molecule. In stokes' lines the lesser frequency is emitted and in the Anti stokes' lines the greater frequency is released. My doubt is: Is the photon completey absorbed by the molecule and the exited molecule gives up a lesser or greater energy in the form of photons (as in the case of fluorescence) or the collided photon itself is simply bounced from the liquid molecule and come out with changed frequencies? In that case what about the energies emitted by the excited molecules themselves while returning to the ground level? Where do they go? Do they also accompany the scattered photons? Also what does a "ground electronic state" exactly stand for? Is it for the K- level of a molecule, ie. the level corresponding to the principal quantum number 1?

Homework Equations

The Attempt at a Solution

 

[ananthu]

Even after several days of posting this question in the forum, I am surprised why I have not got a single reply! Kindly,any one, share your views...

 

[queenofbabes]

If the photon is absorbed, it is completely absorbed, since its energy will match the gap between the energy levels of the atom. When the atom falls back to the ground state, it might not do so in one step, but instead it might have several transition states. If so, at each transition, the energy is released as a photon of lesser energy (than the original incident one).

A photon will not bounce off and have a different frequency.

Ground state is the state of lowest energy, before being excited by the incoming photons.

 

[ananthu]

Thank you for your reply. In one of the texts it is given like this. ie."in fluorescence a photon is completely absorbed whereas it is not so in raman effect". Also in fluoresnce only higher freqency photon is absorbed and the radiation given out is always that of a lower frequency one.. But in raman effect both lower and higher frequencies are given out..
Then how do we exactly differentiate between the two?
Is it that in fluorescence the absorption takes place beteen two real electronic states whereas in the latter the absorption takes place only between vibrational states? So both are the cases of absorptions only?
Is it also possible that an excited atom receives energy from the colliding photon, goes to a higher vibrational state, not an electronic one, returns to the ground state by emitting some infrared lines along with the photon which hit the atom and lost part of its energy? what I mean is that since the infrared emissions can not be seen and therefore we see only the photon bounced with lesser frequency as stokes' line?