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Indian Forest Service (Mains)

Chemistry optional

  • 2 papers
  • 200 marks each
  • 3 h per paper

Paper II covers organic chemistry and spectroscopy.

Indian Forest Service (Mains), Chemistry optional · 2025 · Paper II

Q8(a)(i). CO rotational constant and bond length

Question

The first rotational line of CO is 3.8424 cm⁻¹. Calculate B and bond length using h = 6.625 × 10⁻²⁷ erg s, c = 3 × 10¹⁰ cm s⁻¹ and NA = 6.022 × 10²³.

Answer in brief

B = 1.9212 cm⁻¹ and r ≈ 1.131 Å.

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The full model answer

As written for the answer booklet: the diagram carries the working, the lines stay short. Read here only; it is not offered as a download.

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Topic notes: rotational (microwave) and Raman spectra, with every Civil Services, IFoS and Geo-Scientist PYQ →

Coversrotational spectrum of COrotational constant Brigid rotorbond length from microwave spectrummoment of inertia

All parts of Question 8