Q21 · CSIR-NET Chemistry, December 2011

Paper: CSIR-NET December 2011 · Subject: Physical Chemistry · Chapter: Molecular Spectroscopy · Topic: Molecular Spectroscopy – General · Marks: 2 · Difficulty: Medium

The Q band in the vibrational spectrum of acetylene is observed in the
(a)C-C stretching mode
(b)C-H symmetric stretching mode
(c)Bending mode
(d)C-H antisymmetric stretching mode.
Answer
Answer: C ✓ checked by 4AB · confidence high
Explanation
A Q branch (ΔJ = 0) appears for perpendicular bands, where the vibrational angular momentum is Π. In linear acetylene those are the bending modes (c).

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