Torsional motion quantized

Collision-induced intramolecular vibration-to-rotation energy transfer appears to be inefficient. The evidence for this inference comes from the study of rotational contours in the one collision-induced transition 7 0° in glyoxal. It is found that the emission from 0° has a distribution over rotational transitions that is close to the thermal distribution. But the vibration v-j in glyoxal is a torsional motion, and the axis of torsion very nearly coincides with the smallest axis of inertia of the molecule, so if collision-induced intramolecular vibra-tion-to-rotation transfer were efficient the emission from 0 should have a nonthermal distribution in the quantum number K (which describes quantization of the motion about the smallest axis of inertia). Note, however, that the collision partner used in this experiment was... 

As evidence of the fact that torsional motions are quantized, excitations between the energy levels of a torsion can be observed in the microwave spectra of organic molecules. In fact, a large fraction of the lessons taught... 

We also covered the fact that molecular structures are dynamic, not static. Multiple degrees of vibrational freedom exist—namely, stretches, bends, torsions, etc. Each is quantized and the motions are constrained by a potential surface. For most organic chemistry purposes, only the quantization of bond stretches becomes relevant. The torsional degrees of freedom, when possessing enough energy, lead to the interconversion of conformers, both in acyclic and cyclic systems. The study of these interconversions is called conformational analysis. 

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