Energy Distributions in Cluster Ensembles undergoing Spontaneous Thermal Isomerization

When isolated clusters in a thermal ensemble are able to undergo spontaneous thermal isomerization, that ensemble displays a rich interplay between energy distribution and isomer distribution. On one hand, the ensemble's isomer distribution depends on the energy distribution, with soft, high entropy isomers becoming increasingly dominant at higher temperatures. On the other hand, the energy distribution in the ensemble has one peak for each of the energetically accessible isomers. Depending on the separations, widths and heights of the peaks, the energy distribution can have distinct peaks or be featureless. We have studied the energy distributions in these systems both experimentally and theoretically. In the experiment, isomerization rates are good measures of the average energy of the cluster ensemble. We have studied the energy distributions of Cs 4 I3 − cluster ensembles through dynamics measurements. The experimental results show that the low-electron-binding-energy isomers contribute peaks with lower average total binding energies to the energy distribution of the cluster ensemble. We have used Metropolis Monte Carlo techniques to simulate thermal ensembles of the closely related Cs 4 I4 − cluster. That simulation has identified the structure of each isomer and explained many experiment phenomena. Moreover, the simulation results show that the energy distribution of the cluster ensemble shows little structure due to the small separation between the peaks contributed by isomers. i Finally we present a phenomenon in two-photon photodetachment, which is not quite related with above topics, and give a new explanation based on Franck-Condon factors. The calculations of the potential energy surfaces show that the (NaI) − 3 cluster anion in excited state has very similar potential energy surface to the neutral (NaI) 3 cluster. The photodetachment from the excited cluster anion to the neutral cluster is dominated by the transitions with ∆ν = 0. The measured electron binding energy from two-photon photodetachment remains fairly constant for a wide range of photon energies as observed in the experiment.

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