A diatomic molecules has a moment of inertia I. By Bohr’s quantisation condition, its rotational energy in the nth level (n ≠ 0) is
(1) \(\frac{h^2}{8\pi ^2 In^2}\)
(2) \(\frac{h^2}{8\pi ^2 In}\)
(3) \(\frac{nh^2}{8\pi ^2 I}\)
(4) \(\frac{n^2h^2}{8\pi ^2 I}\)