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UPSC Combined Geo-Scientist

Chemist

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

Mains Paper II covers physical chemistry.

UPSC Combined Geo-Scientist, Mains · 2022 · Mains Paper II

Q15(b). First overtone and hot band in IR spectra

Question

What are 1st overtone and hot band in IR spectroscopy? How can these two be differentiated experimentally?

Answer in brief

1st overtone: v = 0 → 2 at 2ν̃e(1 − 3xe), just under twice the fundamental; hot band: v = 1 → 2 at ν̃e(1 − 4xe), just below it; only the hot band grows on heating.

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Topic notes: vibrational and electronic spectra (force constant, isotope effect, overtones, Franck–Condon), with every Civil Services, IFoS and Geo-Scientist PYQ →

Coversovertonehot bandanharmonic oscillatorIR spectroscopyBoltzmann populationHCl

All parts of Question 15