IGNOU MCH 20 2026 - Raman rotational spectra of was observed with Hg light with

Question

Raman rotational spectra of $\text{H}_2$ was observed with Hg light with Rayleigh line at $2294 \text{ cm}^{-1}$ . Stokes lines were observed at $22581, 22337, 22094, 21851 \text{ cm}^{-1}$ . Draw the rotational energy level diagram with Stokes and anti Stokes lines.

21 Jan 2026

Answer :

Word Count : 294

In Raman spectroscopy, the rotational spectra arise due to changes in the rotational energy of molecules during inelastic scattering of light. When monochromatic light, such as mercury (Hg) lamp emission, interacts with molecules, most photons are elastically scattered, producing the Rayleigh line at the incident frequency. However, a small fraction of light undergoes inelastic scattering, resulting in the Raman lines. In rotational Raman spectra, the scattered photons can either gain energy (anti-Stokes lines) or lose energy (Stokes lines) depending on the initial rotational state of

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