Dissociation pathways and binding energies of lithium clusters from evaporation experiments

Abstract

The unimolecular dissociation of energy rich lithium cluster ions shows that Li+n dissociate by sequential atom or dimer loss. The binding energies of Li+n (n=4–42) generated in an evaporative ensemble are determined from unimolecular decay, within a well defined time window, and energy constraint. They present a sawtooth behavior vs cluster size less pronounced that it should be from a simple metal model. Odd–even alternation is superimposed on the sawtooth behavior, with odd sized cluster ions being more stable. Cohesive energies per atom of Li+n are deduced from these dissociation energies up to n=40 and from extended photo-induced measurements up to n=95. Cohesive energies per atom of neutral clusters Lin are derived by combining these ionic cohesive energies with the literature ionization potentials. The linearity of the neutral cluster cohesive energy vs the cluster surface to volume ratio permits a volume and a surface energy to be deduced. These values are compared to the bulk values.

Decay pathways of small gold clusters

“…The fragmentation pathways of singly charged metal clusters have been studied for several monovalent elements [1][2][3][4][5][6][7][8][9][10][11][12] and are an important tool in understanding cluster energetics and dynamics. After moderate excitation above their dissociation threshold singly charged metal cluster ions show a competition between the evaporation of a single neutral atom and a neutral dimer…”

“…Studies of the alkali-metal clusters Li + n (n = 4-42) [1], Na + n (n = 5-40) [2] and K + n (n = 5-200) [3], and of the monovalent noble metal clusters Cu + n (n = 2-17) [5,12], Ag + n (n = 3-21) [4,6] and Au + n (n = 3-23) [7] show that small odd-numbered clusters of these elements evaporate a neutral dimer while the other cluster sizes evaporate neutral monomers. A similar behavior has also been found for anionic clusters, Cu − n (n = 2-8) [10], Ag − n (n = 2-11) [9] and Au − n (n = 2-15) [8,11].…”

Photodissociation of small group-11 metal cluster ions: Fragmentation pathways and photoabsorption cross sections

“…For most clusters of group-11 metals (copper, silver and gold), neutral monomer evaporation is the only relevant decay pathway. For some cluster sizes, however, neutral dimer evaporation is known to be a strong competitor [1][2][3][4][5][6][7][8][9][10][11][12][13]. This competition can be described in terms of the statistical nature of the unimolecular dissociation process.…”

A combined heating cooling stage for cluster thermalization in the gas phase

“…On the one hand, the cluster can be heated by the absorption of laser light. [1][2][3]13 In this case, several photons of the laser light illuminating the clusters en route are absorbed within a few nanoseconds. The final cluster temperature depends on many parameters, such as the photon energy, laser power, and absorption cross section, and is usually not known.…”

“…Clusters of a particularly stable structure stronger resist this evaporation process and can be identified by a set of pronounced peaks in a mass spectrum taken at elevated temperatures. [1][2][3][4][5] Moreover experiments probing thermodynamic properties require the cluster temperature to be varied in order to melt or thermalize clusters. For instance, well-defined cluster temperatures are necessary for the determination of the heat capacity and melting point of free sodium clusters, [6][7][8] the activation energies and evaporation rate for the evaporation of weakly bound sodium clusters, 9,10 as well as the study of the decay behavior of fullerene dimers.…”