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13 Cards in this Set
- Front
- Back
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Raman spectroscopy is based upon the study of S.......... R..........
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Scattered radiation
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If M......... light is passed through a T.......... substance then a small amount of radiation will be scattered in every direction.
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Monochromatic
Transparent |
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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 |
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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.
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Stokes scattering is...
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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. |
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Anti - Stokes scattering is...
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When the molecular energy is used to excite the incident photon.
This form of scattering is much weaker than Stokes scattering. |
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What is the aim of Raman spectroscopy?
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1) Illuminate the sample with intense monochromatic light
2) Spectrum is obtained by measuring the intensity of scattered radiation. |
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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.
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Why is AC current used in the electric field?
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AC current is oscillating and therefore the induced dipole in the molecule will also oscillate.
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For a vibration to be Raman active it must...
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The polarisability of the molecule must change during the vibration.
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Are diatomic molecules Raman active?
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Yes all diatomics, including heteronuclear and homonuclear molecules.
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What is the selection rule associated with Raman Spec?
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Δv = ±1
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Are polyatomic molecules Raman active?
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Yes, however, beyond triatomic molecules it becomes near impossible due to the complexity, this is the reason for symmetry,
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