Paper: CSIR-NET December 2015 · Subject: Physical Chemistry · Chapter: Group Theory · Topic: Character Tables · Marks: 2 · Difficulty: Medium
The irreducible representations of $\mathrm{C}_{2 \mathrm{h}}$ are $\mathrm{Ag}, \mathrm{B}_{\mathrm{g}}, \mathrm{A}_{\mathrm{u}}$ and $\mathrm{B}_{\mathrm{u}}$. The Raman active modes of trans- 1, 3 butadiene belong to the irreducible representations
(a)$\mathrm{A}_{\mathrm{g}}$ and $\mathrm{B}_{\mathrm{g}}$
(b)$\mathrm{A}_{\mathrm{g}}$ and $\mathrm{A}_{\mathrm{u}}$
(c)$\mathrm{A}_{\mathrm{u}}$ and $\mathrm{B}_{\mathrm{g}}$
(d)$\mathrm{B}_{\mathrm{g}}$ and $\mathrm{B}_{\mathrm{u}}$
Answer
Answer: A ✓ checked by 4AB · confidence high
Explanation
In a centrosymmetric molecule Raman-active modes are gerade: A_g and B_g (A_u and B_u are IR-active) — the mutual exclusion rule.