The UMIST database for astrochemistry 2006

Woodall, Joanna; Agúndez, M.; Markwick-Kemper, A. J.; Millar, T. J.

doi:10.1051/0004-6361:20064981

Cited by 591 publications

(680 citation statements)

References 123 publications

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“…It relies on the availability of comprehensive databases of chemical reaction rate coefficients. Today a few databases are publicly available, such as UDfA 3 (Woodall et al 2007), the Ohio database OSU 4 , and the NIST Chemistry Webbook 5 . There are also efforts to pool all available reaction data into a unified database (KIDA: KInetic Database for Astrochemistry) 6 .…”

Section: Model Chemistrymentioning

confidence: 99%

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Carbon fractionation in photo-dissociation regions

Röllig

Ossenkopf

2013

A&A

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We upgraded the chemical network from the UMIST Database for Astrochemistry 2006 to include isotopes such as 13 C and 18 O. This includes all corresponding isotopologues, their chemical reactions and the properly scaled reaction rate coefficients. We study the fractionation behavior of astrochemically relevant species over a wide range of model parameters, relevant for modelling of photo-dissociation regions (PDRs). We separately analyze the fractionation of the local abundances, fractionation of the total column densities, and fractionation visible in the emission line ratios. We find that strong C + fractionation is possible in cool C + gas. Optical thickness as well as excitation effects produce intensity ratios between 40 and 400. The fractionation of CO in PDRs is significantly different from the diffuse interstellar medium. PDR model results never show a fractionation ratio of the CO column density larger than the elemental ratio. Isotope-selective photo-dissociation is always dominated by the isotope-selective chemistry in dense PDR gas. The fractionation of C, CH, CH + and HCO + is studied in detail, showing that the fractionation of C, CH and CH + is dominated by the fractionation of their parental species. The light hydrides chemically derive from C + , and, consequently, their fractionation state is coupled to that of C + . The fractionation of C is a mixed case depending on whether formation from CO or HCO + dominates. Ratios of the emission lines of [C ii], [C i], 13 CO, and H 13 CO + provide individual diagnostics to the fractionation status of C + , C, and CO.

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Section: Model Chemistrymentioning

confidence: 99%

“…To illustrate how the choice of the chemical data set affects the outcome of our astrochemical calculations we calculate our reference model for three different chemical sets: UDfA06 (Woodall et al 2007), OSU (version osu_01_2009), and KIDA (version kida.uva.2011(version kida.uva. , Wakelam et al 2012.…”

Section: Appendix C: Influence Of Chemical Data Setsmentioning

confidence: 99%

Carbon fractionation in photo-dissociation regions

Röllig

Ossenkopf

2013

A&A

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“…The cations C 2 + and N 2 + , however, are both reactive with H 2 but not with H-atom. The reactivity of O 2 + with either species has not been reported (Woodall et al 2007). As C 2 + may be an important chain carrier for the production of larger carbon molecules (Smith 1992;Oka et al 2003), we turn our attention to the rotational energy distributions in C 2 + as they would appear under conditions in the ISM.…”

Section: Modelling For C 2 + Under Conditions Of the Diffuse And Tranmentioning

confidence: 99%

“…Carbon-containing molecules as large as CH 5 + and C 2 H 2 were included; the C 3 molecule and larger carbon chains were not. All of the rate constants were taken from the most current UMIST database (Woodall et al 2007). …”

Section: Two Cloud Conditions Modelledmentioning

confidence: 99%

On the rotational energy distributions of reactive, non-polar species in the interstellar medium

Glinski

Hoy

Downum

2012

Astrophys Space Sci

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A basic model for the formation of non-equilibrium rotational energy distributions is described for reactive, homo-polar diatomic molecules and ions in the interstellar medium. Kinetic models were constructed to calculate the rotational populations of C 2 + under the conditions it would experience in the diffuse interstellar medium. As the non-polar ion reacts with molecular hydrogen, but not atomic hydrogen, the thermalization of a hot nascent rotational population will be arrested by chemical reaction when the H 2 density begins to be significant. Populations that deviate strongly from the local thermodynamic equilibrium are predicted for C 2 + in environments where it may be detectable. Consequences of this are discussed and a new optical spectrum is calculated.

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“…To estimate the importance of OH and H 2 O formation on dust grains, a comparison is made to the gas phase neutral-neutral formation rates, which are given by (UMIST database: Le Teuff et al 2000;Woodall et al 2007) k OH,gas = 3.14 × 10 −13 T gas 300…”

Section: Oh and H 2 O Formation: Gas Versus Dustmentioning

confidence: 99%

Enhanced H₂O formation through dust grain chemistry in X-ray exposed environments

Meijerink

Cazaux²,

Spaans³

2012

A&A

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Context. The ultraluminous infrared galaxy Mrk 231, which shows signs of both black hole accretion and star formation, exhibits very strong water rotational lines between λ = 200−670 μm, comparable to the strength of the CO rotational lines. High-redshift quasars also show similar CO and H 2 O line properties, while starburst galaxies, such as M 82, lack these very strong H 2 O lines in the same wavelength range, but do show strong CO lines. Aims. We explore the possibility of enhancing the gas phase H 2 O abundance in X-ray exposed environments, using bare interstellar carbonaceous dust grains as a catalyst. Cloud-cloud collisions cause C and J shocks, and strip the grains of their ice layers. The internal UV field created by X-rays from the accreting black hole does not allow reforming the ice. Methods. We determined the formation rates of both OH and H 2 O on dust grains, with temperatures T dust = 10−60 K, using both Monte Carlo and rate equation method simulations. The acquired formation rates were added to our X-ray chemistry code, which allowed us to calculate the thermal and chemical structure of the interstellar medium near an active galactic nucleus. Results. We derive analytic expressions for the formation of OH and H 2 O on bare dust grains as a catalyst. Oxygen atoms arriving on the dust are released into the gas phase in the form of OH and H 2 O. The efficiencies of this conversion due to the chemistry occurring on dust are near 30 percent for oxygen converted into OH and 60 percent for oxygen converted into H 2 O between T dust = 15−40 K. At higher temperatures, the efficiencies decline rapidly. When the gas is mostly atomic, molecule formation on dust is dominant over the gas-phase route, which is then quenched by the low H 2 abundance. Here, it is possible to enhance the warm (T > 200 K) water abundance by an order of magnitude in X-ray exposed environments. This helps explain the observed bright water lines in nearby and high-redshift ULIRGs and quasars.

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The UMIST database for astrochemistry 2006

Cited by 591 publications

References 123 publications

Carbon fractionation in photo-dissociation regions

Carbon fractionation in photo-dissociation regions

On the rotational energy distributions of reactive, non-polar species in the interstellar medium

Enhanced H₂O formation through dust grain chemistry in X-ray exposed environments

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The UMIST database for astrochemistry 2006

Cited by 591 publications

References 123 publications

Carbon fractionation in photo-dissociation regions

Carbon fractionation in photo-dissociation regions

On the rotational energy distributions of reactive, non-polar species in the interstellar medium

Enhanced H2O formation through dust grain chemistry in X-ray exposed environments

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Enhanced H₂O formation through dust grain chemistry in X-ray exposed environments