From Normal Modes through New Modes Born in Chaos to Unimolecular Rearrangement

Mickle Kellman

Department of Chemistry, University of Oregon, Eugene, Oregon 97403, USA

At low energy, molecular vibrations are described by the normal modes approximation. In highly excited vibrational states, chaotic dynamics develop. New modes are born in branchings, or bifurcations of the normal modes. Sometimes, one or more of these new modes evolves into a "reaction mode" for a chemical transformation. I will describe theoretical tools to get this information from analysis of complex experimental spectra, using the vibrational dynamics of highly excited bend states of acetylene as an example. The concept of new modes born in bifurcations is depicted with the aid of easily visualizable computer animations based on analysis of experimental data. Surprising new motions of acetylene are revealed, far different from the ordinary low-energy normal modes.