Q99 · CSIR-NET Chemistry, December 2013

Paper: CSIR-NET December 2013 · Subject: Physical Chemistry · Chapter: Molecular Spectroscopy · Topic: Molecular Spectroscopy – General · Marks: 2 · Difficulty: Medium

The atomic masses of fluorine and hydrogen are 19.0 and 1.0 amu, respectively ( $1 \mathrm{amu}=1.67 \times 10^{-27} \mathrm{kg})$. The bond length of HF is $2.0 \AA$. The moment of inertia of HF is
(a)$3.2 \times 10^{-47} \mathrm{kg} \mathrm{m}^{2}$
(b)$6-4 \times 10^{-47} \mathrm{kg} \mathrm{m}^{2}$
(c)$9-6 \times 10^{-47} \mathrm{kg} \mathrm{m}^{2}$
(d)$4.8 \times 10^{-47} \mathrm{kg\,m^{2}}$
Answer
Answer: B ✓ checked by 4AB · confidence high
Explanation
μ = (19 × 1)/(19 + 1) amu = 0.95 × 1.67×10⁻²⁷ = 1.59×10⁻²⁷ kg; I = μr² = 1.59×10⁻²⁷ × (2.0×10⁻¹⁰)² = 6.3×10⁻⁴⁷ kg m².

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