Introduction to High Resolution Spectroscopy 
Introduction Rotational Vibrational Miscellaneous

Microwave Spectrum Of A Rigid-Rotor Diatomic Molecule
  
 

In microwave spectroscopy, rotational transitions are allowed between adjacent J levels - the selection rule is:

delta j = plus or minus 1

where an increase in J corresponds to absorption and a decrease in J to emission. The transition energy is the difference in the energy between the two levels. If one level has a rotational quantum number of J then absorption is to the level with quantum number J+1. The energy of these levels is:

E=BJ(J+1)

and

energy=b*(j+1)*(j+2)

The energy difference is then:

delta energy=2*b*(j+1)

Input a value into the calculator below for the rotational constant (in cm-1) and press "calculate" to work out the transition energies (in cm-1). The result is a set of lines with separation of 2B.

Once you have covered all of the available resources for rotational spectroscopy, you should test your knowledge and understanding with the self test.


rigid rotor transition energy calculator
 
rotational constant B (cm-1)

  





 
      J                     energy     transition       transition energy (separation) (cm-1)


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