Q131 · CSIR-NET Chemistry, December 2019

Paper: CSIR-NET December 2019 · Subject: Physical Chemistry · Chapter: Molecular Spectroscopy · Topic: Molecular Spectroscopy – General · Marks: 2 · Difficulty: Medium

The molecule with the smallest rotation partition function at any temperature among the following is:

(a)$\mathrm{CH}_{3}-\mathrm{C} \equiv \mathrm{C}-\mathrm{H}$

(b)$\mathrm{H}-\mathrm{C} \equiv \mathrm{C}-\mathrm{H}$

(c)$\mathrm{H}-\mathrm{C} \equiv \mathrm{C}-\mathrm{D}$

(d)$\mathrm{D}-\mathrm{C} \equiv \mathrm{C}-\mathrm{D}$

Answer

Answer: B ✓ checked by 4AB · confidence high

Explanation

q_rot = kT/(σhcB): the smallest q needs the largest B (lightest molecule) and largest σ — acetylene (σ = 2, smallest moment of inertia).

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