Product Energy and Angular Momentum Partitioning in the Unimolecular Dissociation Of Aluminum Clusters

Peslherbe, Gilles H.; Hase, William L.

doi:10.1021/jp0012146

Cited by 61 publications

(33 citation statements)

References 57 publications

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“…If the influence of the rotational angular momentum on the fragmentation probabilities can be verified and quantified, for example, along the lines of Refs. [29,30], this may open up the possibility to determine the amount of angular momentum carried by isolated clusters and to investigate the cooling of their rotational degrees of freedom.…”

Section: Discussionmentioning

confidence: 99%

Competition between delayed ionization and fragmentation of laser-excited Al4−

et al. 2011

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A systematic study of the competition between delayed electron and delayed atom emission from photoexcited Al − 4 clusters was performed using a bent electrostatic ion beam trap, which allows for simultaneous measurement of both decay channels. The aluminum cluster anions, produced with high internal energy in a sputter source, are stored for 100 ms prior to their excitation by a short laser pulse. Delayed ionization and delayed fragmentation were observed for photon energies 1.55 eV < E λ < 2.25 eV. Decay spectra, integrated relative cross sections, and branching ratios were determined as a function of photon energy and storage time. The results show the characteristic pattern expected for a statistical decay ofthe photoexcited Al − 4 clusters; however, the ratio between fragmentation and ionization is found to increase with decreasing photon energy, even though the threshold energy for fragmentation is calculated to be ∼0.5 eV higher than the adiabatic electron detachment energy. It is suggested that the tetramers, while cooling down in the trap, may be in long-lived excited configurations with lower effective fragmentation barriers; Al − 4 clusters carrying high rotational angular momenta are discussed as possible candidates. Results obtained for other aluminum clusters Al − n (5 n 9) are also reported.

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Section: Discussionmentioning

confidence: 99%

Competition between delayed ionization and fragmentation of laser-excited Al4−

et al. 2011

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“…A useful alternative technique lies in statistical rate theories, which can be quantitative provided that anharmonicities are accounted for. 9,11 Here we use the Weisskopf approach from nuclear physics, 41 which is of comparable accuracy as phase space theory for non-rotating systems. 10 According to this theory, the dissociation rate k X corresponding to the emission of X particles can be cast as 10,41 …”

Section: Statistical Dissociationmentioning

confidence: 99%

“…Thermal dissociation of finite clusters offers such an opportunity, as the related observables of rate constants or kinetic energy released are intimately connected to the statistical properties through the densities of states (DOSs). 8,9 Earlier investigations on small rare-gas 9, 10 or metallic 11 clusters have shown that statistical rate theories can be made accurate against numerically exact molecular dynamics simulations if the densities of states are carefully evaluated including anharmonicity effects. In those works, the residual discrepancies could be attributed to the poor knowledge of the absolute DOSs, rather than manifestations of non-ergodicity.…”

Section: Introductionmentioning

confidence: 99%

Evidence for broken ergodicity due to chemical alloying from the dissociation kinetics of binary clusters

Calvo

Yurtsever

2014

The Journal of Chemical Physics

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The interplay between thermal relaxation and statistical dissociation in binary Morse clusters (AB)N has been investigated using numerical simulations and simple statistical approaches, for a variety of interaction parameters covering miscible and non-miscible regimes. While all clusters exhibit a core/shell phase separation pattern in their most stable, T = 0 structure, different melting mechanisms are identified depending on the ranges and their mismatch, including two-step melting of the surface and the core or premelting as alloying. The preference for emitting A or B particles upon evaporation has been evaluated assuming that the cluster is either thermally equilibrated or vibrationally excited in its ground state structure, and compared to the predictions of the Weisskopf theory. The variations of the dissociation rate constants with increasing energy and the branching ratio between the two channels show significant differences in both cases, especially when the clusters are miscible and bound by short-range forces, which indicates that the time scale for evaporation is much shorter than the equilibration time. Our results suggest that dissociation properties could be used to test the ergodic hypothesis in such compounds.

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“…In contrast to this, other aspects of dissociation kinetics of metal clusters are now modeled with great sophistication using both statistical theories and the methods of molecular dynamics. [39][40][41] …”

Section: Introductionmentioning

confidence: 99%

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

Shvartsburg

Siu

2001

The Journal of Chemical Physics

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Articles you may be interested inDissociation of internal energy-selected methyl bromide ion revealed from threshold photoelectron-photoion coincidence velocity imaging Hydrogen exchange kinetics in NaAlH 4 catalyzed in different decomposition states J. Appl. Phys. 95, 7748 (2004); 10.1063/1.1751634 Excited-state diffusion-influenced reversible association-dissociation reaction: Brownian dynamics simulation in three dimensionsModeling the delayed dissociation of clusters had been over the last decade a frontline development area in chemical physics. It is of fundamental interest how statistical kinetics methods previously validated for regular molecules and atomic nuclei may apply to clusters, as this would help to understand the transferability of statistical models for disintegration of complex systems across various classes of physical objects. From a practical perspective, accurate simulation of unimolecular decomposition is critical for the extraction of true thermochemical values from measurements on the decay of energized clusters. Metal clusters are particularly challenging because of the multitude of low-lying electronic states that are coupled to vibrations. This has previously been accounted for assuming the average electronic structure of a conducting cluster approximated by the levels of electron in a cavity. While this provides a reasonable time-averaged description, it ignores the distribution of instantaneous electronic structures in a ''boiling'' cluster around that average. Here we set up a new treatment that incorporates the statistical distribution of electronic levels around the average picture using random matrix theory. This approach faithfully reflects the completely chaotic ''vibronic soup'' nature of hot metal clusters. We found that the consideration of electronic level statistics significantly promotes electronic excitation and thus increases the magnitude of its effect. As this excitation always depresses the decay rates, the inclusion of level statistics results in slower dissociation of metal clusters.

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Product Energy and Angular Momentum Partitioning in the Unimolecular Dissociation Of Aluminum Clusters

Cited by 61 publications

References 57 publications

Competition between delayed ionization and fragmentation of laser-excited Al4−

Competition between delayed ionization and fragmentation of laser-excited Al4−

Evidence for broken ergodicity due to chemical alloying from the dissociation kinetics of binary clusters

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

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