New Theoretical Results Concerning the Interstellar Abundance of Molecular Oxygen

Quan, Donghui; Herbst, Eric; Millar, T. J.; Hassel, G. E.; Lin, Shi Ying; Guo, Hua; Honvault, Pascal; Xie, Daiqian

doi:10.1086/588007

Cited by 32 publications

(39 citation statements)

References 32 publications

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“…The abundance of OH increases with density, in line with that of O (see, e.g., Harju et al 2000;Quan et al 2008). Thus, after the freeze-out of CO, the reaction CO + OH could proceed on the ice mantle due to higher abundances of CO on the grain surface.…”

Section: Astrophysical Implicationsmentioning

confidence: 70%

CO₂FORMATION IN QUIESCENT CLOUDS: AN EXPERIMENTAL STUDY OF THE CO + OH PATHWAY

Noble¹,

Dulieu²,

Congiu³

et al. 2011

ApJ

114

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The formation of CO 2 in quiescent regions of molecular clouds is not yet fully understood, despite CO 2 having an abundance of around 10%-34% H 2 O. We present a study of the formation of CO 2 via the nonenergetic route CO + OH on nonporous H 2 O and amorphous silicate surfaces. Our results are in the form of temperature-programmed desorption spectra of CO 2 produced via two experimental routes: O 2 + CO + H and O 3 + CO + H. The maximum yield of CO 2 is around 8% with respect to the starting quantity of CO, suggesting a barrier to CO + OH. The rate of reaction, based on modeling results, is 24 times slower than O 2 + H. Our model suggests that competition between CO 2 formation via CO + OH and other surface reactions of OH is a key factor in the low yields of CO 2 obtained experimentally, with relative reaction rates ofAstrophysically, the presence of CO 2 in low A V regions of molecular clouds could be explained by the reaction CO + OH occurring concurrently with the formation of H 2 O via the route OH + H.

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Section: Astrophysical Implicationsmentioning

confidence: 70%

CO₂FORMATION IN QUIESCENT CLOUDS: AN EXPERIMENTAL STUDY OF THE CO + OH PATHWAY

Noble¹,

Dulieu²,

Congiu³

et al. 2011

ApJ

114

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“…1 [57,58], referred to as the XXZLG PES. The XX-ZLG PES has been used in a number of quantum dynamics calculations of the O + OH system at high collision energies [53,54,59]. The present DIMKP PES was employed for the first time for this reaction in our previous work [33] and it is preferred at low energies as it includes accurate long-range coefficients.…”

Section: Methodology a Potential Energy Surfacesmentioning

confidence: 99%

Formation of molecular oxygen in ultracoldO+OHcollisions

2009

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We discuss the formation of molecular oxygen in ultracold collisions between hydroxyl radicals and atomic oxygen. A time-independent quantum formalism based on hyperspherical coordinates is employed for the calculations. Elastic, inelastic and reactive cross sections as well as the vibrational and rotational populations of the product O2 molecules are reported. A J-shifting approximation is used to compute the rate coefficients. At temperatures T = 10 − 100 mK for which the OH molecules have been cooled and trapped experimentally, the elastic and reactive rate coefficients are of comparable magnitude, while at colder temperatures, T < 1 mK, the formation of molecular oxygen becomes the dominant pathway. The validity of a classical capture model to describe cold collisions of OH and O is also discussed. While very good agreement is found between classical and quantum results at T = 0.3 K, at higher temperatures, the quantum calculations predict a larger rate coefficient than the classical model, in agreement with experimental data for the O + OH reaction. The zero-temperature limiting value of the rate coefficient is predicted to be about 6 × 10 −12 cm 3 molecule −1 s −1 , a value comparable to that of barrierless alkali-metal atom -dimer systems and about a factor of five larger than that of the tunneling dominated F + H2 reaction.

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“…Quéméner et al (2009) have determined that the reaction still proceeds in the limit of zero temperature with a rate coefficient of approximately 6 × 10 −12 cm 3 s −1 . Quan et al (2008) re-examined the sensitivity of the interstellar O 2 abundance to the low-temperature behaviour of the source reaction.…”

Section: O 18 O Column Density and O 18 O Abundancementioning

confidence: 99%

$O^{18}$O and $C^{18}$O observations ofρOphiuchi A

Liseau¹,

Larsson²,

Bergman³

et al. 2010

A&A

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Context. Contrary to theoretical expectation, surprisingly low concentrations of molecular oxygen, O 2 , have been found in the interstellar medium. Telluric absorption makes ground based O 2 observations essentially impossible and observations had to be done from space. Millimetre-wave telescopes on space platforms were necessarily small, which resulted in large, several arcminutes wide, beam patterns. Observations of the (N J = 1 1 −1 0 ) ground state transition of O 2 with the Odin satellite resulted in a 5σ detection toward the dense core ρ Oph A. At the frequency of the line, 119 GHz, the Odin telescope has a beam width of 10 , larger than the size of the dense core.Aims. The precise nature of the emitting source and its exact location and extent are therefore unknown. The current investigation is intended to remedy this. Methods. Although the Earth's atmosphere is entirely opaque to low-lying O 2 transitions, it allows ground based observations of the much rarer 16 O 18 O in favourable conditions and at much higher angular resolution with larger telescopes. In addition, ρ Oph A exhibits both multiple radial velocity systems and considerable velocity gradients. Extensive mapping of the region in the proxy C 18 O (J = 3−2) line can be expected to help identify the O 2 source on the basis of its line shape and Doppler velocity. Line opacities were determined from observations of optically thin 13 C 18 O (J = 3−2). During several observing periods, two C 18 O intensity maxima in ρ Oph A were searched for O 18 O in the (2 1 −0 1 ) line at 234 GHz with the 12 m APEX telescope. These positions are associated also with peaks in the mm-continuum emission from dust.

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New Theoretical Results Concerning the Interstellar Abundance of Molecular Oxygen

Cited by 32 publications

References 32 publications

CO₂FORMATION IN QUIESCENT CLOUDS: AN EXPERIMENTAL STUDY OF THE CO + OH PATHWAY

CO₂FORMATION IN QUIESCENT CLOUDS: AN EXPERIMENTAL STUDY OF THE CO + OH PATHWAY

Formation of molecular oxygen in ultracoldO+OHcollisions

$O^{18}$O and $C^{18}$O observations ofρOphiuchi A

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New Theoretical Results Concerning the Interstellar Abundance of Molecular Oxygen

Cited by 32 publications

References 32 publications

CO2FORMATION IN QUIESCENT CLOUDS: AN EXPERIMENTAL STUDY OF THE CO + OH PATHWAY

CO2FORMATION IN QUIESCENT CLOUDS: AN EXPERIMENTAL STUDY OF THE CO + OH PATHWAY

Formation of molecular oxygen in ultracoldO+OHcollisions

$O^{18}$O and $C^{18}$O observations ofρOphiuchi A

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Product

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CO₂FORMATION IN QUIESCENT CLOUDS: AN EXPERIMENTAL STUDY OF THE CO + OH PATHWAY

CO₂FORMATION IN QUIESCENT CLOUDS: AN EXPERIMENTAL STUDY OF THE CO + OH PATHWAY