Aluminum clusters: ionization thresholds and reactivity toward deuterium, water, oxygen, methanol, methane, and carbon monoxide

Abstract

Using the pulsed cluster beam flow reactor technique, we have measured the reactivity of aluminum clusters toward several molecules under thermal conditions. For each different molecule we observe that the reactivity exhibits a unique dependence on the number of aluminum atoms in the cluster. The overall reactivity of aluminum clusters toward different molecules is ordered roughly as 02 > CH3OH > CO > D20 > D2 > CH4 with CH4 showing no reaction under these experimental conditions. In addition, we are able to place upper and lower bounds on the ionization thresholds for the smaller aluminum clusters.

Predictions of melting, crystallization, and local atomic arrangements of aluminum clusters using a reactive force field

“…The DFT calculations for Al 5 are consistent with the works of Yang et al 9 In addition, Pettersson et al 1 found that in the case of Al 6 the octahedron is the most stable form, whereas Upton 2 found a distorted octahedron to be the most stable. Clearly, for Al clusters with more than five atoms three dimensional ͑3D͒ structures are favored since as the size of the clusters increases the number of nearest neighbors also increases, but this cannot be achieved in a planar structure.…”

“…Upon heating the rhombus structure it immediately transforms into the tetrahedron isomer even at temperatures of as low as 1 K. The tetrahedron structure was also found by Böyükata and Güvenç, 47 who used the embedded atom method ͑EAM͒, 48 to be the most stable isomer of Al 4 . For Al 5 DFT favors the planar rhombus ͑C 2v ͒-like structure ͓Fig. 3͑c͔͒, in agreement with Pettersson et al 1 but ReaxFF finds the trigonal bipyramidal ͑D 3h ͒ isomer ͓Fig.…”

“…5 Other theoretical computations [6][7][8][9][10][11] have tackled issues to do with the energetically lowest structures of small aluminum clusters, although even for small clusters such as Al 4 , Al 5 , and Al 7 there are still lingering uncertainties on the preferred configurations. The other point of interest is the existence of magic clusters ͑superatoms͒ of aluminum.…”

Dissociation of multiple hydrogen molecules on the non-planar aluminium cluster: stationary points on the Al6 + nH2 potential energy surface

“…For the light metals like aluminium this type of reactions is of potential technological importance for hydrogen storage. In the early gas phase experimental studies of the reactions of aluminium clusters with molecular hydrogen of Cox et al [4], it was observed that the onset of reactivity of Al n towards H 2 occured for hexamer Al 6 (n=6). Recently, by using mass spectrometry and photoelectron spectroscopy (PE) techniques, Li et al [5][6] studied the series of new aluminium hydride anions Al n H n+2 -(4≤n≤8) and, by analyzing the recorded PE spectra, they drew conclusions on the electronic properties and stability of the corresponding neutral alanes Al n H n+2 .…”

Quantum Monte Carlo study of small aluminum clusters Aln(n=2–13)

“…6,10,11 In last years, several experimental and theoretical studies have been carried out to obtain the IP, EA, and DE of Al n clusters as a function of their atomic size (number of atoms). Experimentally, they are usually obtained by using pulsed cluster beam flow reactor 12 and photoelectron spectroscopy techniques. [13][14][15] Theoretical calculations are mostly based on density functional theory.…”