IR Spectra: Why is CO2 a doublet at 2350cm-1?

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    Co2 Ir Spectra
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SUMMARY

CO2 exhibits a doublet peak at 2350 cm-1 due to Fermi resonance, a phenomenon where the interaction between vibrational modes leads to the appearance of two distinct peaks. Despite being a linear molecule, CO2 demonstrates this doublet as a result of its vibrational characteristics, specifically involving symmetric and asymmetric stretching modes. This behavior is consistent with the principles outlined in IR spectroscopy and is a classical example of Fermi resonance.

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  • Understanding of IR spectroscopy principles
  • Familiarity with molecular vibrations and stretching modes
  • Knowledge of linear molecular geometry
  • Basic concepts of Fermi resonance in spectroscopy
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  • Study "vibrational modes of linear molecules" to understand molecular behavior
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Chemists, students of physical chemistry, and researchers interested in molecular spectroscopy and vibrational analysis will benefit from this discussion.

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CO2 is supposed to create a "doublet" peak at 2350 cm-1 according to my IR correlation chart. Why is this doublet created? As DrDu explained in my previous post, two peaks are seen for the N-O bond because it has IR-active symmetric and asymmetric stretches. But CO2 is a linear molecule, and thus should not have an IR-active symmetric stretch.

I found another post on this forum in which chemistree explains the doublet as resulting from "symmetric and asymmetric" stretching, but that doesn't make sense to me considering the above. Does anyone know why the CO2 doublet exists? Thank you!
 
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