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  Rotational Raman Spectroscopy
Centrifugal Distortion page 2 of 3
Practical Navigator
The Raman Effect
Experimental Techniques
1. Rotational Raman Spectroscopy
Interpreting the Spectrum
Effect of Bond Length
Centrifugal Distortion
Intensities of Spectral Lines
Nuclear Spin Statistics
2. Real Diatomic Molecules
Spectrum of Nitrogen
Isotopic Substitution
Nuclear Spin Statistics
Predict the Spectrum of Oxygen
  To the left of the spectra window there is a button labelled Centrifugal Distortion. Clicking on this brings up a window. The value of D is initially zero as in the Rigid Rotor Model. Moving the slider varies the value of D for .

Moving the slider to the right sets D as positive. Move the slider slowly increasing D positively. See how this changes the rotational energy levels of .

Q3.6 How does this affect the spectra? Why do the Stokes lines move closer together and the Anti-Stokes lines move further apart?

In some molecules the centrifugal constant is large enough that spectral lines appear on top of each other. Ultimately a sequence of lines can reach a "band head" and then reverse direction. Applet 2 shows an example of this.

Q3.7 Describe what has happened to the energy levels to produce two overlapping spectral lines.
Q3.8 What are the J values for the two lines that occur on top of each other?
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