Thursday, October 13, 2011

A concrete test of the Morse potential in a complex molecule

Just how accurate is the Morse potential? A key feature is the equidistance of adjacent energy levels.
This graph below illustrates the high quality of the Morse potential for describing a C=O bond within a protein. The data (taken from this PNAS paper) is via a technique which induces transitions from the v'th vibrational energy level to the (v+1) level.

Thus we see the Morse potential describes the true anharmonic potential at least up to v=7, which corresponds to energies of about 1.5 eV above that of the potential minimum.

This success also underscores the local character of these bond stretching vibrations.


  1. Are you sure the second sentence here isn't about the harmonic oscillator, not the Morse oscillator. Don't the energy gaps get smaller as you go up the Morse oscillator?

  2. I can reply since I was fooled in the same way,
    but the reading carefully the caption of fig.1...

    it is not the difference between the energy levels which is equidistant in the Morse potential, but the difference in consecutive transitions.