Q10. Vibrational spectrum of CO₂: expected and observed
CO₂ is a linear triatomic molecule. How many lines do you expect to have in its vibrational spectrum? Compare this with the observed IR spectrum of CO₂.
Answer in brief
4 normal modes, 3 fundamentals (ν₂ doubly degenerate): IR 667 and 2349 cm⁻¹, Raman 1388 cm⁻¹; the observed IR shows these two, none at 1388, plus weak extra bands.
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CoversCO₂ normal modesIR spectrumRaman spectrumrule of mutual exclusionFermi resonance3N − 5