Rotational energy levels — UPSC CSE 2022 Physics PYQ

(i) In a diatomic molecule when one constituent atom is replaced by one of its heavier isotopes, what change takes place in the rotational spectrum?

(ii) Calculate the change in rotational constant B when hydrogen is replaced by deuterium in the hydrogen molecule.

(iii) Draw the spectra of rigid and non-rigid rotors by using the schematic representation of the rotational energy levels and comment on it.