Electronic structure investigation of neutral titanium oxide molecules TixOy

Jeong, K. S.; Chang, Ch.; Sedlmayr, E.; Sülzle, Detlev

doi:10.1088/0953-4075/33/17/319

Cited by 89 publications

(130 citation statements)

References 34 publications

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“…Geometry of the calculated (TiO 2 ) N structures. Molecules labelled "a" are the molecules calculated by Jeong et al (2000) and those labelled "b" or unlabelled are the current most stable cluster geometries (Calatayud et al 2008;Syzgantseva et al 2011). Grey balls represent Ti atoms while red represent O atoms.…”

Section: Computational Aspectsmentioning

confidence: 99%

Dust in brown dwarfs and extra-solar planets

Lee

Helling

Giles

et al. 2015

A&A

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Context. Clouds form in atmospheres of brown dwarfs and planets. The cloud particle formation processes, seed formation and growth/evaporation are very similar to the dust formation process studied in circumstellar shells of AGB stars and in supernovae. Cloud formation modelling in substellar objects requires gravitational settling and element replenishment in addition to element depletion. All processes depend on the local conditions, and a simultaneous treatment is required. Aims. We apply new material data in order to assess our cloud formation model results regarding the treatment of the formation of condensation seeds. We look again at the question of the primary nucleation species in view of new (TiO 2 ) N -cluster data and new SiO vapour pressure data. Methods. We applied the density functional theory (B3LYP, 6-311G(d)) using the computational chemistry package G 09 to derive updated thermodynamical data for (TiO 2 ) N clusters as input for our TiO 2 seed formation model. We tested different nucleation treatments and their effect on the overall cloud structure by solving a system of dust moment equations and element conservation for a prescribed D-P atmosphere structure. Results. Updated Gibbs free energies for the (TiO 2 ) N clusters are presented, as well as a slightly temperature dependent surface tension for T = 500 . . . 2000 K with an average value of σ ∞ = 480.6 erg cm −2 . The TiO 2 seed formation rate changes only slightly with the updated cluster data. A considerably larger effect on the rate of seed formation, and hence on grain size and dust number density, results from a switch to SiO nucleation. The question about the most efficient nucleation species can only be answered if all dust/cloud formation processes and their feedback are taken into account. Despite the higher abundance of SiO over TiO 2 in the gas phase, TiO 2 remains considerably more efficient at forming condensation seeds by homogeneous nucleation. The paper discusses the effect on the cloud structure in more detail.

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Section: Computational Aspectsmentioning

confidence: 99%

Dust in brown dwarfs and extra-solar planets

Lee

Helling

Giles

et al. 2015

A&A

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“…(34) in Helling & Woitke (2006), applying the modified classical nucleation theory of Gail et al (1984). We use the value of the surface tension σ fitted to small cluster data by Jeong et al (2000) as outlined in Woitke & Helling (2004).…”

Section: Dust Seed Formationmentioning

confidence: 99%

Dust in brown dwarfs and extra-solar planets

Witte¹,

Helling²,

Hauschildt³

2009

A&A

124

168

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Context. Substellar objects have extremely long life spans. The cosmological consequence for older objects are low abundances for heavy elements, which in turn results in a wide distribution of objects over metallicity, hence over age. Within their cool atmosphere, dust clouds become a dominant feature, affecting the opacity and the remaining gas phase abundance of heavy elements. Aims. We investigate the influence of the stellar metallicity on the dust formation in substellar atmospheres and on the dust cloud structure and its feedback on the atmosphere. This work has implications for the general questions of star formation and of dust formation in the early universe. Methods. We utilise numerical simulations to solve a set of moment equations to determine the quasi-static dust cloud structure (Drift). These equations model the nucleation, the kinetic growth of composite particles, their evaporation, and the gravitational settling as a stationary dust formation process. Element conservation equations augment this system of equations by including the element replenishment by convective overshooting. The integration with an atmosphere code (Phoenix) allows determination of a consistent (T, p, v conv )-structure (T -local temperature, p -local pressure, v conv -convective velocity), hence, to calculate synthetic spectra. Results. A grid of Drift-Phoenix model atmospheres was calculated for a wide range of metallicity, [M/H] ∈ [+0.5, −0.0, −0.5, ..., −6.0], to allow for systematic study of atmospheric cloud structures throughout the evolution of the universe. We find dust clouds in even the most metal-poor ([M/H] = −6.0) atmosphere of brown dwarfs. Only the most massive among the youngest brown dwarfs and giant gas planets can resist dust formation. For very low heavy element abundances, a temperature inversion develops that has a drastic impact on the dust cloud structure. Conclusions. The combination of metal depletion by dust formation and the uncertainty of interior element abundances makes the modelling of substellar atmospheres an intricate problem in particular for old substellar objects. We furthermore show that the dust-togas ratio does not scale linearly with the object's [M/H] for a given effective temperature. The mean grain sizes and the composition of the grains change depending on [M/H], which influences the dust opacity that determines radiative heating and cooling, as well as the spectral appearance.

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“…The surface tension for the nucleating clusters are determined from size dependent thermodynamical data (see e.g. Jeong et al 2000). For (TiO 2 ) N a surface tension of σ = 800 erg cm −2 is adopted (Jeong 2000, priv.…”

Section: Complex Bmentioning

confidence: 99%

“…The dust grains are core-mantle grains with a homogeneous core of (TiO 2 ) N (Gail & Sedlmayr 1998;Jeong 2000) and a heterogeneous mantel composed of SiO and TiO 2 . The thermodynamic data for the (TiO 2 ) N cluster have been obtained from density functional quantum mechanical model calculations by Jeong et al (2000). The dust opacity is treated in the small particle limit of Mie theory.…”

Section: Numerical Featuresmentioning

confidence: 99%

Dust in brown dwarfs

Helling

Oevermann

Lüttke

et al. 2001

A&A

106

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Abstract. Dust formation in turbulent media is studied adopting the example of brown dwarf atmospheres. By combining asymptotic techniques and time-dependent, multi-dimensional numerical simulations, we show that acoustic waves originating from convective motions provide a mechanism to initiate dust nucleation in otherwise dust-hostile environments. The subsequently growing particles cause a radiative cooling strong enough to reinitiate efficient dust formation resulting in a strongly inhomogeneous distribution of dust in such environments. Recent observations bear indications for such cloudy dust distributions in brown dwarf atmospheres.

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Electronic structure investigation of neutral titanium oxide molecules Ti_xO_y

Cited by 89 publications

References 34 publications

Dust in brown dwarfs and extra-solar planets

Dust in brown dwarfs and extra-solar planets

Dust in brown dwarfs and extra-solar planets

Dust in brown dwarfs

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