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Labham posted an Question
November 15, 2019 • 13:02 pm 15 points
  • IIT JAM
  • Chemistry (CY)

What is difference between rigid rotator and non rigid rotator?

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    Eduncle Best Answer

    Answer - 

    To develop a description of the rotational states, we will consider the molecule to be a rigid object, i.e. the bond lengths are fixed and the molecule cannot vibrate. This model for rotation is called the rigid-rotor model. It is a good approximation (even though a molecule vibrates as it rotates, and the bonds are elastic rather than rigid) because the amplitude of the vibration is small compared to the bond length.
     
    If the shape of the molecule is allowed to distort upon rotation, then the restriction of the rigid rotor is lifted. It may be expected that as the rotational energy increases the molecule will have it's bond lengthened because of the centrifugal distortion. This will lead to an effective decrease in the rotational energy since the longer bond will lead to a decrease in the rotational energy. We can refine the theory by adding correction term, containing the centrifugal distortion constant, D, which corrects for the fact that the bond is not rigid. 
     
    F(J) = BJ(J+ 1) - DJ^2(J +1)^2 

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    what's centrifugal distortion ?

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