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Gross and Specific Selection rules for different molecular spectroscopies


  • Gross selection rule tells whether a molecule will be active or inactive in a particular Spectroscopy.

 

  • Specific selection rule tells about the allowed changes in the magnitude of energy when it is active in a particular Spectroscopy.

 

  1.  Rotational or Microwave Spectroscopy

  • Gross selection rule: permanent dipole moment 
  • Specific selection rule: ∆J = +1 or -1 ( for rigid rotor)


2.Vibrational or IR Spectroscopy
  • Gross selection rule: change in dipole moment during vibrations
  • Specific selection rule: ∆v = +1 or -1 ( for harmonic oscillator)


3. Raman Spectroscopy
  • Gross selection rule: change in polarizability 
  • Specific selection rule:

  •   ∆J = 0, +2 or -2 
    •  ∆v = +1 or -1 


    4. Electronic or UV-Visible Spectroscopy
    • Gross selection rule: No stringent rule
    • Specific selection rule: ∆s = 0  and ∆l = +1 or -1


    5. Nuclear Magnetic  Resonance or Radio waves Spectroscopy
    • Gross selection rule: nuclear spin should be no zero 
    • Specific selection rule: ∆m = +1 or -1
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