Dissociation kinetics of metal clusters on multiple electronic states including electronic level statistics into the vibronic soup

Modeling the delayed dissociation of clusters had been over the last decade a frontline development area in chemical physics. It is of fundamental int erest how statistical kinetics methods previously validated for regular mol ecules and atomic nuclei may apply to clusters, as this would help to under stand the transferability of statistical models for disintegration of compl ex systems across various classes of physical objects. From a practical per spective, accurate simulation of unimolecular decomposition is critical for the extraction of true thermochemical values from measurements on the deca y of energized clusters. Metal clusters are particularly challenging becaus e of the multitude of low-lying electronic states that are coupled to vibra tions. This has previously been accounted for assuming the average electron ic structure of a conducting cluster approximated by the levels of electron in a cavity. While this provides a reasonable time-averaged description, i t ignores the distribution of instantaneous electronic structures in a "boi ling" cluster around that average. Here we set up a new treatment that inco rporates the statistical distribution of electronic levels around the avera ge picture using random matrix theory. This approach faithfully reflects th e completely chaotic "vibronic soup" nature of hot metal clusters. We found that the consideration of electronic level statistics significantly promot es electronic excitation and thus increases the magnitude of its effect. As this excitation always depresses the decay rates, the inclusion of level s tatistics results in slower dissociation of metal clusters. (C) 2001 Americ an Institute of Physics.