At low energy, the internal motion of molecules can be described as the familiar normal modes. At higher energy, the normal modes approximation breaks down, due to anharmonic (nonlinear) dynamics. This results in birth of new anharmonic modes in bifurcations, and the onset of widespread chaotic classical dynamics.

In a bifurcation, a normal mode changes character, with an abrupt change in the natural motions of the molecule. This results in severe disturbance of the ordinary spectral patterns associated with normal modes.

In our group we obtain information about the natural motions of molecules by “decoding” the information contained in the spectroscopic Hamiltonian used to fit experimental data. In a sense, we have a spectroscopic window on the ultrafast internal dynamics.

On the next page, you will find a bifurcation diagram for the bending motions of C₂H₂ (acetylene). You can click on different points of the diagram, and see an animation of the molecular motion represented there. You will find some very surprising types of motion abstracted from the experimental spectra.

You can scroll down on the next page to a detailed explanation below the diagram. Before reading the explanation, you may want to just click on the animations first!

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In case of slow modem connection, you may wish to download a compressed version of the whole webpage (kellmanlab.zip, size 760kb) on your hard drive. Then click here .

Click here to read Vivian Ding's Ph.D. thesis, completed in March 2004.

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