Q30 · CSIR NET Chemistry, December 2016
Paper: CSIR NET December 2016 · Subject: Physical Chemistry · Chapter: Molecular Spectroscopy · Topic: Molecular Spectroscopy – General · Marks: 2 · Difficulty: Medium
The rotational constant and the fundamental vibrational frequency of HBr are, respectively, $10\,\mathrm{cm^{-1}}$ and $2000\,\mathrm{cm^{-1}}$. The corresponding values for DBr approximately are
(a)$20\,\mathrm{cm^{-1}}$ and $2000\,\mathrm{cm^{-1}}$
(b)$10\,\mathrm{cm^{-1}}$ and $1410\,\mathrm{cm^{-1}}$
(c)$5\,\mathrm{cm^{-1}}$ and $2000\,\mathrm{cm^{-1}}$
(d)$5\,\mathrm{cm^{-1}}$ and $1410\,\mathrm{cm^{-1}}$
Answer
Answer: D ✓ checked by 4AB · confidence high
Explanation
μ(DBr) ≈ 2μ(HBr): B halves to ≈5 cm⁻¹ and ν falls by √2 to ≈1410 cm⁻¹ (d).
Study loop for Molecular Spectroscopy