Deuterium fractionation along the TMC-1 ridge

Markwick, A. J.; Charnley, Steven B.; Millar, T. J.

doi:10.1051/0004-6361:20011022

Cited by 20 publications

(19 citation statements)

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“…Furthermore, it is unclear if models such as that presented here could explain the observed spatial abundance gradients seen in TMC-1. Gradients of complex molecule abundances and deuterium fractionation ratios also appear to be better matched in the models of Markwick et al (Markwick et al , 2001a. These considerations fit into the overall picture of star-formation regulating the physics and chemistry of clumpy molecular clouds, as proposed by Norman & Silk (1980).…”

Section: Conclusion and Discussionsupporting

confidence: 71%

Gas-grain chemical models of star-forming molecular clouds as constrained by ISO and SWAS observations

Charnley

Rodgers

Ehrenfreund

2001

A&A

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110

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Abstract.We have investigated the gaseous and solid state molecular composition of dense interstellar material that periodically experiences processing in the shock waves associated with ongoing star formation. Our motivation is to confront these models with the stringent abundance constraints on CO2, H2O and O2, in both gas and solid phases, that have been set by ISO and SWAS. We also compare our results with the chemical composition of dark molecular clouds as determined by ground-based telescopes. Beginning with the simplest possible model needed to study molecular cloud gas-grain chemistry, we only include additional processes where they are clearly required to satisfy one or more of the ISO-SWAS constraints. When CO, N2 and atoms of N, C and S are efficiently desorbed from grains, a chemical quasi-steady-state develops after about one million years. We find that accretion of CO2 and H2O cannot explain the [CO2/H2O]ice ISO observations; as with previous models, accretion and reaction of oxygen atoms are necessary although a high O atom abundance can still be derived from the CO that remains in the gas. The observational constraints on solid and gaseous molecular oxygen are both met in this model. However, we find that we cannot explain the lowest H2O abundances seen by SWAS or the highest atomic carbon abundances found in molecular clouds; additional chemical processes are required and possible candidates are given. One prediction of models of this type is that there should be some regions of molecular clouds which contain high gas phase abundances of H2O, O2 and NO. A further consequence, we find, is that interstellar grain mantles could be rich in NH2OH and NO2. The search for these regions, as well as NH2OH and NO2 in ices and in hot cores, is an important further test of this scenario. The model can give good agreement with observations of simple molecules in dark molecular clouds such as TMC-1 and L134N. Despite the fact that S atoms are assumed to be continously desorbed from grain surfaces, we find that the sulphur chemistry independently experiences an "accretion catastrophe". The S-bearing molecular abundances cease to lie within the observed range after about 3 × 10 6 years and this indicates that there may be at least two efficient surface desorption mechanisms operating in dark clouds -one quasi-continous and the other operating more sporadically on this time-scale. We suggest that mantle removal on short time-scales is mediated by clump dynamics, and by the effects of star formation on longer time-scales. The applicability of this type of dynamical-chemical model for molecular cloud evolution is discussed and comparison is made with other models of dark cloud chemistry.

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Section: Conclusion and Discussionsupporting

confidence: 71%

Gas-grain chemical models of star-forming molecular clouds as constrained by ISO and SWAS observations

Charnley

Rodgers

Ehrenfreund

2001

A&A

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110

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“…Besides the gasphase ion chemistry, the subject of this paper, there may be rather efficient neutral reactions involving radicals (Kaiser 2002). In addition, there is plenty of room for speculation about the chemistry occurring in and on grain ice mantles; there is observational evidence that deuterated carbonaceous species are released from the solid phase into the gas phase (Markwick et al 2001(Markwick et al , 2002. In order to explore in more detail astrochemically important reactions involving carbon atoms and molecules, a specific research program has been started in our laboratory based on ion trapping and atomic and molecular beams (Č ermák et al 2002;G.…”

Section: New Routes In Formingghydrocarbons and Deuterated Variantsmentioning

confidence: 99%

Low‐Temperature Experiments on the Formation of Deuterated C₃H⁺₃

Savić¹,

Gerlich²

2005

ApJ

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“…Hirahara et al 1992;Hartquist et al 1996;Pratap et al 1997). Alternative views have been presented by Hartquist et al (1996) who discuss the possibility that the CP peak is highly depleted and represents a chemically more advanced stage than the NH 3 peak, and by Markwick et al (2000Markwick et al ( , 2001 who suggest that carbon chemistry at the CP peak has been revived by evaporation of carbon bearing mantle species (CH 4 , C 2 H 2 , C 2 H 4 ) following grain-grain collisions induced by the ion-neutral slip produced by the passage of an A&A 531, A121 (2011) Alfvén wave. In this model, complex organic species are not necessarily coincident with the most rudimentary forms of carbon.…”

Section: Introductionmentioning

confidence: 99%

CH abundance gradient in TMC-1

Suutarinen

Geppert

Harju

et al. 2011

A&A

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Aims. The aim of this study is to examine if the well-known chemical gradient in TMC-1 is reflected in the amount of rudimentary forms of carbon available in the gas-phase. As a tracer we use the CH radical which is supposed to be well correlated with carbon atoms and simple hydrocarbon ions. Methods. We observed the 9-cm Λ-doubling lines of CH along the dense filament of TMC-1. The CH column densities were compared with the total H 2 column densities derived using the 2MASS NIR data and previously published SCUBA maps and with OH column densities derived using previous observations with Effelsberg. We also modelled the chemical evolution of TMC-1 adopting physical conditions typical of dark clouds using the UMIST Database for Astrochemistry gas-phase reaction network to aid the interpretation of the observed OH/CH abundance ratios. Results. The CH column density has a clear peak in the vicinity of the cyanopolyyne maximum of TMC-1. The fractional CH abundance relative to H 2 increases steadily from the northwestern end of the filament where it lies around 1.0 × 10 −8 , to the southeast where it reaches a value of 2.0 × 10 −8 . The OH and CH column densities are well correlated, and we obtained OH/CH abundance ratios of ∼16-20. These values are clearly larger than what has been measured recently in diffuse interstellar gas and is likely to be related to C to CO conversion at higher densities. The good correlation between CH and OH can be explained by similar production and destruction pathways. We suggest that the observed CH and OH abundance gradients are mainly due to enhanced abundances in a low-density envelope which becomes more prominent in the southeastern part and seems to continue beyond the dense filament.Conclusions. An extensive envelope probably signifies an early stage of dynamical evolution, and conforms with the detection of a large CH abundance in the southeastern part of the cloud. The implied presence of other simple forms of carbon in the gas phase provides a natural explanation for the observation of "early-type" molecules in this region.

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Deuterium fractionation along the TMC-1 ridge

Cited by 20 publications

References 19 publications

Gas-grain chemical models of star-forming molecular clouds as constrained by ISO and SWAS observations

Gas-grain chemical models of star-forming molecular clouds as constrained by ISO and SWAS observations

Low‐Temperature Experiments on the Formation of Deuterated C₃H⁺₃

CH abundance gradient in TMC-1

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Deuterium fractionation along the TMC-1 ridge

Cited by 20 publications

References 19 publications

Gas-grain chemical models of star-forming molecular clouds as constrained by ISO and SWAS observations

Gas-grain chemical models of star-forming molecular clouds as constrained by ISO and SWAS observations

Low‐Temperature Experiments on the Formation of Deuterated C3H+3

CH abundance gradient in TMC-1

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Low‐Temperature Experiments on the Formation of Deuterated C₃H⁺₃