Editing Rotational spectroscopy (section)

===Effect of vibration on rotation===
The population of vibrationally excited states follows a [[Boltzmann distribution]], so low-frequency vibrational states are appreciably populated even at room temperatures. As the moment of inertia is higher when a vibration is excited, the rotational constants (''B'') decrease. Consequently, the rotation frequencies in each vibration state are different from each other. This can give rise to "satellite" lines in the rotational spectrum. An example is provided by [[cyanodiacetylene]], H−C≡C−C≡C−C≡N.<ref>{{cite journal|last=Alexander|first=A. J.|author2=Kroto, H. W. |author3=Walton, D. R. M. |title=The microwave spectrum, substitution structure and dipole moment of cyanobutadiyne|journal=J. Mol. Spectrosc.|date=1967|volume=62|issue=2|pages=175–180|doi=10.1016/0022-2852(76)90347-7|bibcode = 1976JMoSp..62..175A }} Illustrated in {{harvnb|Hollas|1996|p=97}}</ref>

Further, there is a [[fictitious force]], [[Coriolis effect|Coriolis coupling]], between the vibrational motion of the nuclei in the rotating (non-inertial) frame. However, as long as the vibrational quantum number does not change (i.e., the molecule is in only one state of vibration), the effect of vibration on rotation is not important, because the time for vibration is much shorter than the time required for rotation. The Coriolis coupling is often negligible, too, if one is interested in low vibrational and rotational quantum numbers only.