Three-phase chemical models of dense interstellar clouds: gas, dust particle mantles and dust particle surfaces

Hasegawa, T.; Herbst, Eric

doi:10.1093/mnras/263.3.589

Cited by 301 publications

(271 citation statements)

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“…On the basis of this limited sample, HOCN may be as widespread as HNCO. Current astrochemical gas-grain model calculations efficiently produce HNCO on grain surfaces by hydrogenation of accreted OCN (Hasegawa & Herbst 1993;Garrod et al 2008). The observed fairly constant abundance ratio of HOCN relative to HNCO in our sample of sources, which is far from thermodynamical equilibrium considering the low temperatures prevalent in the interstellar medium 2 , suggests that HOCN is formed along with HNCO on the grain mantles, and then subsequently released through shocks or during warm-up.…”

Section: Discussionmentioning

confidence: 70%

Interstellar HOCN in the Galactic center region

Brünken¹,

Беллоче

Martín

et al. 2010

A&A

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Aims. Our aim is to confirm the interstellar detection of cyanic acid, HOCN, in the Galactic center clouds. It has previously been tentatively detected only in Sgr B2(OH). Methods. We used a complete line survey of the hot cores Sgr B2(N) and (M) in the 3 mm range, complemented by additional observations carried out with the IRAM 30 m telescope at selected frequencies in the 2 mm band and towards four additional positions in the Sgr B2 cloud complex in the 2 and 3 mm bands. The spectral survey was analysed in the local thermodynamical equilibrium approximation (LTE) by modeling the emission of all identified molecules simultaneously. This allowed us to distinguish weak features of HOCN from the rich line spectrum observed in Sgr B2(N) and (M). Lines of the more stable (by 1.1 eV) isomer isocyanic acid, HNCO, in these sources, as well as those of HOCN and HNCO towards the other positions, were analysed in the LTE approximation as well. Results. Four transitions of HOCN were detected in a quiescent molecular cloud in the Galactic center at a position offset in (RA, Dec) by (20 , 100 ) from the hot core source Sgr B2(M), confirming its previous tentative interstellar detection. Up to four transitions were detected toward five other positions in the Sgr B2 complex, including the hot cores Sgr B2(M), (S), and (N). A fairly constant abundance ratio of ∼0.3−0.8% for HOCN relative to HNCO was derived for the extended gas components, suggesting a common formation process of these isomers.

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Section: Discussionmentioning

confidence: 70%

Interstellar HOCN in the Galactic center region

Brünken¹,

Беллоче

Martín

et al. 2010

A&A

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“…We used a chemical model integrated in a 3-phase system similar that of Hasegawa & Herbst (1993b). The three phases are gas, grain surface, and grain mantle.…”

Section: Model Considerationsmentioning

confidence: 99%

“…They conclude that photoprocessing of grain mantles is the start of the synthesis of many species. Hasegawa & Herbst (1993b) use a 3-phase model to examine the formation and composition of the inner mantle. They found that radicals like OH, CH 3 etc.…”

Section: Introductionmentioning

confidence: 99%

Subsurface chemistry of mantles of interstellar dust grains in dark molecular cores

Kalvāns¹,

Shmeld²

2010

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Context. The abundances of many observed compounds in interstellar molecular clouds still lack an explanation, despite extensive research that includes both gas and solid (dust-grain surface) phase reactions. Aims. We aim to qualitatively prove the idea that a hydrogen-poor subsurface chemistry on interstellar grains is responsible for at least some of these chemical "anomalies". This chemistry develops in the icy mantles when photodissociation reactions in the mantle release free hydrogen, which escapes the mantle via diffusion. This results in serious alterations of the chemical composition of the mantle because pores in the mantle provide surfaces for reactions in the new, hydrogen-poor environment.Methods. We present a simple kinetic model, using existing astrochemical reaction databases. Gas phase, surface and subsurface pore reactions are included, as are physical transformations of molecules. Results. Our model produces significantly higher abundances for various oxidized species than most other models. We also obtain quite good results for some individual species that have adequate reaction network. Thus, we consider that the hydrogen-poor mantle chemistry may indeed play a role in the chemical evolution of molecular clouds. Conclusions. The significance of outward hydrogen diffusion has to be proved by further research. A huge number of solid phase reactions between many oxidized species is essential to obtain good, quantitative modeling results for a comparison with observations. We speculate that a variety of unobservable hydrogen-poor sulfur oxoacid derivatives may be responsible for the "disappearance" of sulfur in dark cloud cores.

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“…the procedure by Hasegawa & Herbst (1993). The abundance of molecular ions such as HCO + , N 2 H + and corresponding deuterated isotopomers are given by the steady state chemical equations using the istantaneous abundances of neutral species.…”

Section: A Simple Chemical Model In a Centrally Concentrated Corementioning

confidence: 99%

Observations of L1521F: A highly evolved starless core

Crapsi

Caselli

Walmsley

et al. 2004

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161

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Abstract. We observed the pre-stellar core L1521F in dust emission at 1.2 mm and in two transitions each of N 2 H + , N 2 D + , C 18 O and C 17 O in order to increase the sample of well studied centrally concentrated and chemically evolved starless cores, likely on the verge of star formation, and to determine the initial conditions for low-mass star formation in the Taurus Molecular Cloud. The dust observation allows us to infer the density structure of the core and together with measurements of CO isotopomers gives us the CO depletion. N 2 H + and N 2 D + lines are good tracers of the dust continuum and thus they give kinematic information on the core nucleus. We derived in this object a molecular hydrogen number density n(H 2 ) ∼ 10 6 cm −3 and a CO depletion factor, integrated along the line of sight, f D ≡ 9.5 × 10 −5 /x obs (CO) ∼ 15 in the central 20 , similar to the pre-stellar core L1544. However, the N(N 2 D + )/N(N 2 H + ) column density ratio is ∼0.1, a factor of about 2 lower than that found in L1544. The observed relation between the deuterium fractionation and the integrated CO depletion factor across the core can be reproduced by chemical models if N 2 H + is slightly (factor of ∼2 in fractional abundance) depleted in the central 3000 AU. The N 2 H + and N 2 D + linewidths in the core center are ∼0.3 km s −1 , significantly larger than in other more quiescent Taurus starless cores but similar to those observed in the center of L1544. The kinematical behaviour of L1521F is more complex than seen in L1544, and a model of contraction due to ambipolar diffusion is only marginally consistent with the present data. Other velocity fields, perhaps produced by accretion of the surrounding material onto the core and/or unresolved substructure, are present. Both chemical and kinematical analyses suggest that L1521F is less evolved than L1544, but, in analogy with L1544, it is approaching the "critical" state.

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Three-phase chemical models of dense interstellar clouds: gas, dust particle mantles and dust particle surfaces

Cited by 301 publications

References 0 publications

Interstellar HOCN in the Galactic center region

Interstellar HOCN in the Galactic center region

Subsurface chemistry of mantles of interstellar dust grains in dark molecular cores

Observations of L1521F: A highly evolved starless core

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