Unexpected Structures of Aluminum Oxide Clusters in the Gas Phase

Sierka, Marek; Döbler, Jens; Sauer, Joachim; Santambrogio, Gabriele; Brümmer, Mathias; Wöste, L.; Janssens, Ewald; Meijer, Gerard; Asmis, Knut R.

doi:10.1002/anie.200604823

Cited by 121 publications

(141 citation statements)

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“…13). The predicted spectra compare well with the experimental results by Demyk et al (2004) and the calculated linear infrared absorption spectra by Sierka et al (2007) for small cluster sizes (see Fig. 14), with the strongest peaks in the 10-11 µm region and an ensemble of smaller peaks around 14 µm.…”

Section: Discussion: Indication For the Presence Of Aluminium Oxide Csupporting

confidence: 82%

“…Demyk et al (2004) and Sierka et al (2007) measured the IR-REMPI spectra of laboratory-produced AlO·(Al 2 O 3 ) n clusters down to n = 7, whereas Li & Cheng (2012) provided structures for a selection of alumina clusters obtained from density functional theory (DFT) calculations. Because there is no way to currently predict the most likely cluster composition in the outflow and because these clusters would probably cover a wide range in both stoichiometry and atomic sizes, we took the simple approach of calculating the spectral properties of a range of stoichiometric alumina clusters to estimate where observable lines might exist.…”

Section: Discussion: Indication For the Presence Of Aluminium Oxide Cmentioning

confidence: 99%

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Study of the aluminium content in AGB winds using ALMA

Decin

Richards

Waters

et al. 2017

A&A

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Context. The condensation of inorganic dust grains in the winds of evolved stars is poorly understood. As of today, it is not yet known which molecular clusters form the first dust grains in oxygen-rich (C/O < 1) asymptotic giant branch (AGB) winds. Aluminium oxides and iron-free silicates are often put forward as promising candidates for the first dust seeds. Aims. We aim to constrain the dust formation histories in the winds of oxygen-rich AGB stars. Methods. We obtained Atacama Large Millimeter/sub-millimeter array (ALMA) observations with a spatial resolution of 120 × 150 mas tracing the dust formation region of the low mass-loss rate AGB star, R Dor, and the high mass-loss rate AGB star, IK Tau. We detected emission line profiles of AlO, AlOH, and AlCl in the ALMA data and used these line profiles to derive a lower limit of atomic aluminium incorporated in molecules. This constrains the aluminium budget that can condense into grains. Results. Radiative transfer models constrain the fractional abundances of AlO, AlOH, and AlCl in IK Tau and R Dor. We show that the gas-phase aluminium chemistry is completely different in both stars with a remarkable difference in the AlO and AlOH abundance stratification. The amount of aluminium locked up in these three molecules is small, ≤1.1 × 10 −7 w.r.t. H 2 , for both stars, i.e. only ≤2% of the total aluminium budget. An important result is that AlO and AlOH, which are the direct precursors of alumina (Al 2 O 3 ) grains, are detected well beyond the onset of the dust condensation, which proves that the aluminium oxide condensation cycle is not fully efficient. The ALMA observations allow us to quantitatively assess the current generation of theoretical dynamical-chemical models for AGB winds. We discuss how the current proposed scenario of aluminium dust condensation for low mass-loss rate AGB stars within a few stellar radii from the star, in particular for R Dor and W Hya, poses a challenge if one wishes to explain both the dust spectral features in the spectral energy distribution (SED) in interferometric data and in the polarized light signal. In particular, the estimated grain temperature of Al 2 O 3 is too high for the grains to retain their amorphous structure. We advocate that large gas-phase (Al 2 O 3 ) n clusters (n > 34) can be the potential agents of the broad 11 µm feature in the SED and in the interferometric data and we propose potential formation mechanisms for these large clusters.

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Section: Discussion: Indication For the Presence Of Aluminium Oxide Csupporting

confidence: 82%

Section: Discussion: Indication For the Presence Of Aluminium Oxide Cmentioning

confidence: 99%

Study of the aluminium content in AGB winds using ALMA

Decin

Richards

Waters

et al. 2017

A&A

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“…For DFT structure prediction, the potential energy surface (PES) is searched first for the global minimum structures with a genetic algorithm 43,44 using the BP86 functional 45,46 together with the split-valence polarized basis set SVP 47 (denoted BP86/SVP). The genetic algorithm run is repeated three times for 500 structures, after which convergence is checked.…”

Section: Methodsmentioning

confidence: 99%

Gas phase structures and charge localization in small aluminum oxide anions: Infrared photodissociation spectroscopy and electronic structure calculations

Song

Fagiani

Gewinner

et al. 2016

The Journal of Chemical Physics

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We use cryogenic ion trap vibrational spectroscopy in combination with quantum chemical calculations to study the structure of mono-and dialuminum oxide anions. The infrared photodissociation spectra of D 2 -tagged AlO 1-4 − and Al 2 O 3-6 − are measured in the region from 400 to 1200 cm −1 . Structures are assigned based on a comparison to simulated harmonic and anharmonic IR spectra derived from electronic structure calculations. The monoaluminum anions contain an even number of electrons and exhibit an electronic closed-shell ground state. The Al 2 O 3-6 − anions are oxygen-centered radicals. As a result of a delicate balance between localization and delocalization of the unpaired electron, only the BHLYP functional is able to qualitatively describe the observed IR spectra of all species with the exception of AlO 3 − . Terminal Al-O stretching modes are found between 1140 and 960 cm −1 . Superoxo and peroxo stretching modes are found at higher (1120-1010 cm −1 ) and lower energies (850-570 cm −1 ), respectively. Four modes in-between 910 and 530 cm −1 represent the IR fingerprint of the common structural motif of dialuminum oxide anions, an asymmetric four-member Al-(O) 2 -Al ring. Published by AIP Publishing. [http://dx

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“…The ECP accounts for core electrons 1s to 3d and includes scalar relativistic effects. The GA applied to generate candidate structures has been described in Sierka et al (2007). Since computational demands for the GA are appreciable, a smaller split valence basis was used to obtain a population of neutral clusters.…”

Section: Tin Cluster Anions: From Spherical To Prolate To Clusters Ofmentioning

confidence: 99%

“…This is not a viable procedure for larger clusters and one needs an unbiased structure search. Several techniques have been proposed and tested for this purpose, and we just mention simulated annealing (Kirkpatrick et al 1983), basin hopping (Wales & Doye 1997) and genetic algorithms (GAs; Hartke 1993;Deaven & Ho 1995;Sierka et al 2007). All these procedures require a large number of single-point calculations or geometry optimizations, which limits their application to relatively small clusters with approximately 30 atoms.…”

Section: Introductionmentioning

confidence: 99%

Quantum chemical treatments of metal clusters

Weigend

Ahlrichs

2010

Phil. Trans. R. Soc. A.

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This work focuses on finding and rationalizing the building principles of clusters with approximately 300 atoms of different types of metals: main group elements (Al, Sn), alkaline earth metals (Mg), transition metals (Pd) and clusters consisting of two different elements (Ir and Pt). Two tools are inevitable for this purpose: (i) quantum chemical methods that are able to treat a given cluster with both sufficient accuracy and efficiency and (ii) algorithms that are able to systematically scan the (3n−6)-dimensional potential surface of an n-atomic cluster for promising isomers. Currently, the only quantum chemical method that can be applied to metal clusters is density functional theory (DFT). Other methods either do not account for the multi-reference character of metal clusters or are too expensive and thus can be applied only to clusters of very few atoms, which usually is not sufficient for studying the building principles. The accuracy of DFT is not known a priori, but extrapolations to bulk values from calculated series of data show satisfying agreement with experimental data. For scans of the potential surface, simulated annealing techniques or genetic algorithms were used for the smaller clusters (approx. 20-30 atoms), and for the larger clusters considerations were restricted to selected packings and shapes. For the mixed-metallic clusters, perturbation theory turned out to be efficient and successful for finding the most promising distributions of the two atom types at the different sites.

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Unexpected Structures of Aluminum Oxide Clusters in the Gas Phase

Abstract: No Abstrac

Cited by 121 publications

References 34 publications

Study of the aluminium content in AGB winds using ALMA

Study of the aluminium content in AGB winds using ALMA

Gas phase structures and charge localization in small aluminum oxide anions: Infrared photodissociation spectroscopy and electronic structure calculations

Quantum chemical treatments of metal clusters

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