ISOMERIZATION DYNAMICS OF NA4CL4 CLUSTERS

In this paper, we explore the cube reversible ladder reversible ring isomerization kinetics (see eq 2) of Na4Cl4 Clusters using RRKM calculations and (constant-energy) molecular dynamics (MD) quenching simulations for the evaluation of the individual rate coefficients for this multistep process. Rotational effects and centrifugal corrections, which are absent in MD simulations, exhibit marked effects on the RRKM rate coefficients, resulting in the enhancement of the forward rate coefficient k1. In the MD simulations, the isomerization was induced by nonselective kinetic energy excitation, with all the velocities of the ions being scaled up by a uniform numerical factor. A detailed comparison between the four rate coefficients obtained from MD simulations (for zero angular momentum) and the statistical harmonic RRKM calculations (without rotational effects) reveals that for k1, k3, and k4 over the entire energy domain and for k2 at low energies, the RRKM rate coefficients exceed the MD rate coefficients. However, the general trends of the energy dependence of the RRKM and MD rate coefficients are similar. Finally, we have investigated the intracluster vibrational energy redistribution (IVR) under our nonselective kinetic energy excitation conditions, which do not strictly correspond to energy equipartitioning among all normal modes. At low energies (at least up to 20000 cm-1), the separation between fast IVR and slow reaction is applicable. At high energies, the conventional description of statistical kinetics breaks down for the nonselective kinetic energy excitation when both the IVR and the reaction time scales approach a common lower limit, which corresponds to a (average) vibrational period.