Molecular spectra — UPSC IFoS 2025 Physics PYQ

(i) With suitable diagrams, explain the intensity distribution of spectral lines in vibrational-electronic spectra by using the Franck-Condon principle. (ii) Calculate the positions of the first two rotational Raman lines in the spectrum of \text{H}_2, if its bond length is 0\cdot 074\text{ nm}. [Given : {}^{1}\text{H} = 1\cdot 673 \times 10^{-27}\text{ kg}]