Introduction to High Resolution Spectroscopy 

Introduction Rotational Vibrational Miscellaneous

Microwave Spectrum Of A Non-Rigid Rotor Diatomic Molecule

The rotational energy levels (in cm-1) for the non-rigid-rotor diatomic are given by the formula:


The first term relates to the energy levels of the rigid rotor and the second term corrects this for the effect of the bond length increasing as the molecular rotates. D is the centrifugal distortion constant and is related to the rotational constant B and the harmonic vibrational frequency, w,of the bond:


Input values into the calculator below for the rotational constant, B, and the vibrational frequency, w, and press "calculate" to work out the energy levels.

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

non-rigid rotor energy level calculator

B (cm-1) w (cm-1) D (cm-1)

      J       rigid rotor non-rigid rotor

© A.J. Bridgeman, School of Chemistry 2023 | Last Modified 10/07/19
School of Chemistry, Building F11, The University of Sydney, NSW 2006, Australia, Ph: +61-2-9351-4504; Fax: +61-2-9351-3329