ORIGIN OF THE COMPLEX DYNAMICS IN STRUCTURAL ISOMERIZATION OF SMALL CLUSTERS - THE EFFECTS OF POTENTIAL TOPOGRAPHY

The dependence of Lifetime distribution in isomerization dynamics of A r-7-like clusters on the potential topography is reported. Using the s caled Morse potential V=Sigma(i<j)(e(-2(rho ij-rho 0)) -2e(-(rho ij-rh o 0))), where rho(ij) is an internuclear distance, and rho(0), the equ ilibrium distance of the isolated diatomic molecule, is the only indep endent parameter that uniquely specifies the system Hamiltonian, we ha ve examined the dynamics for two typical values of rho(0). In the high enough energy region, which is called the liquidlike phase, the clust er of a small po (called a compact cluster) has an exponential form fo r the lifetime distribution. In contrast, dynamics on the potential wi th a large po (a loose cluster) exhibits a large deviation from the ex ponential form, its mixing dynamics notwithstanding; it displays a lar ge hole in the short lifetime region and a steep clifflike structure i n the even shorter lifetime region embedded in the hole. Since the dev iation is so clear, the present system offers an excellent example wit h which to investigate the dependence of phase space structure on the potential topography. We have identified the mechanisms of formation b oth of the hole and cliff. The hole is particularly important to under stand how mixing dynamics can deviate from the statistically simple ex ponential distribution. By comparing a variety of quantities that char acterize the system dynamics, we propose a conceptual picture to under stand the basic difference between the dynamics on compact and loose p otentials, in which the complexity of the dynamics is ascribed to the bifurcation of the reaction tubes and to the turning-point distributio ns clinging to the branching places of such bifurcated tubes. (C) 1998 American Institute of Physics.