Comment on the Raman activity of the symmetric stretching mode of the
fundamental vibrations of carbon dioxide molecule. Give explanation.
Answers
Answer:
Molecules with 3 or more atoms can vibrate in more complex patterns. A single molecule can vibrate in various ways; each of these different motions is called a vibration "mode". Carbon dioxide (CO2) molecules have three different vibration modes
Molecules with more (and more complex!) vibration modes are more likely to interact with passing waves of electromagnetic radiation. This is why carbon dioxide absorbs and emits infrared (IR) radiation, while nitrogen and oxygen molecules do not. This ability to absorb infrared waves is what makes carbon dioxide a greenhouse gas.
Water vapor (H2O) and methane (CH4) molecules also have vibration modes that cause them to interact with passing IR waves. As you might expect, methane and water vapor are also greenhouse gase
Explanation:
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Answer:
The Raman optical activity (ROA) method of vibrational spectroscopy relies on the molecule chirality-related differential in Raman scattered light's right and left circular polarisation intensities.
Explanation:
Due to the constant net molecule dipole, the symmetric stretch of carbon dioxide is not IR active. Both bonds are more readily polarisable because they have been stretched (or extended). The symmetric stretch is Raman active, and there are general changes in molecule polarizability.
The net molecular dipole changes, making the asymmetric stretch of carbon dioxide IR active. One bond is stretched and becomes more polarizable in the asymmetric stretch, while the other bond is compressed and becomes less polarizable. The shorter bond precisely compensates for the change in the long bond's polarizability, maintaining the molecule's constant total polarizability. The asymmetric stretch is therefore not Raman active.
The change in the net molecule dipole makes the bending motion of carbon dioxide IR active. No changes in bond length or the polarizability of the molecule result from the bending action. The bending motion is not, thus, Raman active.
Hence, due to the constant net molecule dipole, the symmetric stretch of carbon dioxide is not IR active.
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