Vibration-rotation band
In infrared spectroscopy the fundamental vibrational absorption and emission transitions of a molecule have components corresponding to molecular rotation.
If the spectrometer has a good resolution (better than 0.5 cm-1), these vibration-rotation bands can be resolved, e.g. for gases at low pressures. At lower resolution the infrared bands appear as broad envelopes, e.g. for liquids and solids.