Rotational Spectra of Diatomic Molecules

[Vaibhav DixiT]

I was wondering how Rotational Spectra of diatomic molecule can be related to Heisenberg Uncertainty principle (Qualitatively). Being a QM model where rotational energies are quantized, there should be a qualitative reasoning on lines of the uncertainty principle, right? Anyone can direct me to a good source? or maybe enlighten me if you know t

 

[BvU]

Uncertainty principle is immediately related to spectral line broadening due to finite lifetime of the excited state. A simple $$\Delta E \Delta t \ge {\hbar\over 2} \ ,$$so quite quantitative, actually.
Rotational energy levels are very close together ($\approx$ 10^-3 eV), compared to vibrational ($\approx$ 10^-1 eV) and electronic (several eV). So you need very high resolution spectroscopy and provisions to eliminate other sources of line broadening (e.g. Doppler).

The energy differences show up in http://www.dsf.unica.it/~sandro/Materiale_Corso/Molec/haken_wolf_Raman.pdf (and here -- a bit hefty), or in
rotation-vibration spectroscopy in the infrared range
Purely rotational spectroscopy is in the microwave range; I don't know much about that.