Lyapunov exponents for the intramolecular motion of the Cl^--CH₃Br complex

The intramolecular dynamics of Cl^-- - -CH₃Br complexes is studied at an energy approximately equal to the average thermal energy of complexes formed by Cl^- + CH₃Br association at 300 K. Lyapunov exponents are calculated for different mode excitations of the Cl^-- - -CH₃Br complex. Without zero-point energy added to the complex, a number of the mode excitations have zero Lyapunov exponents and, thus, regular motion. The Lyapunov exponents are positive and the motion is chaotic for all mode excitations with zero-point energy added. However, the latter Lyapunov exponents are sufficiently small that the time required to form a microcanonical ensemble of Cl^-- - -CH₃Br states is much longer than the RRKM lifetime of the complex. Thus, non-RRKM unimolecular dynamics is expected for the Cl^-- - -CH₃Br complex as found in previous trajectory simulations.