Effect of the internal rotation of the OH group on the OH stretching vibrational Raman profile of ethanol in the gas phase

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Abstract
A quantum mechanical calculation was performed to explain the temperature dependence of the OH stretching vibrational Raman profile of ethanol, which mainly consists in a pronounced increase in scattering intensity on the central region between the two band components caused by rotational isomerism. Introducing the interaction between the stretching vibrational and internal rotational motions of the OH group by means of the angular dependence of the OH stretching frequency, which can be directly taken from the gauche–trans splitting of the OH band in the experimental spectrum, leads to the result that the ‘‘fill‐up’’ effect observed in the central region can be attributed to vibrational transitions between excited torsional states.