UPSC Combined Geo-Scientist, Mains · 2021 · Mains Paper II
Q15(a). The J = 6 → 7 line from the J = 3 → 4 line of a rigid rotor
Question
The J = 3 → 4 transition for a diatomic molecule occurs at 0.50 cm⁻¹. What is the wave number for the J = 6 → 7 transition for this molecule? Assume the molecule is a rigid rotor.
Answer in brief
ν̃(J→J+1) = 2B(J + 1): 8B = 0.50 cm⁻¹ gives B = 0.0625 cm⁻¹, so ν̃(6→7) = 14B = 0.875 cm⁻¹.
Part of VKC Basic
Read the key points and the full model answer with VKC Basic
VKC Basic (₹999 for 6 months) opens every solved answer, the notes, the handbook and the daily answer archive. Every Mains test series includes it.
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.
The handwritten model answer pages open with the VKC plan.
Coversrigid rotorrotational spectrumrotational constantmicrowave spectroscopymoment of inertia
All parts of Question 15
- 15(a) The J = 6 → 7 line from the J = 3 → 4 line of a rigid rotor10 marks
- 15(b) Normal modes of CS₂ and OCS; IR activity5 marks
- 15(c) Why saturated KCl or NH₄NO₃ in a salt bridge5 marks