Q72 · CSIR NET Chemistry, December 2017
Paper: CSIR NET December 2017 · Subject: Physical Chemistry · Chapter: Molecular Spectroscopy · Topic: Vibrational · Marks: 2 · Difficulty: Medium
The normal mode of ethylene represented, by the figure below, is 
(a)only IR active
(b)only Raman active
(c)both IR and Raman active
(d)neither IR nor Raman active
Answer
Answer: B ✓ checked by 4AB · confidence medium
Explanation
The drawn H motion is the in-plane CH₂ rocking/twisting mode of g symmetry. It is centrosymmetric, so it is Raman-only (b, chapter key).
Study loop for Molecular Spectroscopy