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13 Cards in this Set

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Raman spectroscopy is based upon the study of S.......... R..........
Scattered radiation
If M......... light is passed through a T.......... substance then a small amount of radiation will be scattered in every direction.
Monochromatic

Transparent
Rayleigh scattering is described as...

(Hint: rubber band)
Where light is scattered elastically, i.e. the photon energies of incoming and scattered light is the same.

This is why the sky is blue
Raman scattering is described as...

Which transitions cause this?
Where the energy of the photons is higher or lower than that of the incident radiation. This scattering is inelastic and is caused by vibrational and rotational transitions.
Stokes scattering is...
When the incident photon energy is used to excite the molecule to a higher vibrational energy level.

This yields a photon of lower energy than the incident photon.
Anti - Stokes scattering is...
When the molecular energy is used to excite the incident photon.

This form of scattering is much weaker than Stokes scattering.
What is the aim of Raman spectroscopy?
1) Illuminate the sample with intense monochromatic light
2) Spectrum is obtained by measuring the intensity of scattered radiation.
Mechanism of Raman scattering...

(Hint: P)
Polarisability is the measure of the ease of which electrons can be displaced relative to the nuclei when a molecule is placed in an electric field.
Why is AC current used in the electric field?
AC current is oscillating and therefore the induced dipole in the molecule will also oscillate.
For a vibration to be Raman active it must...
The polarisability of the molecule must change during the vibration.
Are diatomic molecules Raman active?
Yes all diatomics, including heteronuclear and homonuclear molecules.
What is the selection rule associated with Raman Spec?
Δv = ±1
Are polyatomic molecules Raman active?
Yes, however, beyond triatomic molecules it becomes near impossible due to the complexity, this is the reason for symmetry,