Molecular Photodissociation

Dishoeck, E. F. van; Visser, R.

doi:10.1002/9783527653133.ch4

Cited by 13 publications

(19 citation statements)

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“…a factor of 10 to 100 higher than in the gas phase (van Dishoeck et al (1996); Boonman et al (2003)). The large amount of CO2 in the gas phase could be produced by the evaporation or destruction of the icy grain mantles (van Dishoeck et al 1996). Comparing the observed gas and ice phase CO2 abundance ratio with those of other species (e.g.…”

Section: Introductionmentioning

confidence: 86%

“…In the solid phase, the observed abundance for CO2 is of the order of 10 −5 to 10 −6 relative to H2 (Gerakines et al 1999), e.g. a factor of 10 to 100 higher than in the gas phase (van Dishoeck et al (1996); Boonman et al (2003)). The large amount of CO2 in the gas phase could be produced by the evaporation or destruction of the icy grain mantles (van Dishoeck et al 1996).…”

Section: Introductionmentioning

confidence: 94%

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Detection of HOCO+ in the protostar IRAS 16293−2422

Majumdar

Gratier

Wakelam

et al. 2018

Monthly Notices of the Royal Astronomical Society

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The protonated form of CO 2 , HOCO + , is assumed to be an indirect tracer of CO 2 in the millimeter/submillimeter regime since CO 2 lacks a permanent dipole moment. Here, we report the detection of two rotational emission lines (4 0,4 -3 0,3 and 5 0,5 -4 0,4 ) of HOCO + in IRAS 16293-2422. For our observations, we have used EMIR heterodyne 3 mm receiver of the IRAM 30m telescope. The observed abundance of HOCO + is compared with the simulations using the 3-phase NAUTILUS chemical model. Implications of the measured abundances of HOCO + to study the chemistry of CO 2 ices using JWST-MIRI and NIRSpec are discussed as well.

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Section: Introductionmentioning

confidence: 86%

Section: Introductionmentioning

confidence: 94%

Detection of HOCO+ in the protostar IRAS 16293−2422

Majumdar

Gratier

Wakelam

et al. 2018

Monthly Notices of the Royal Astronomical Society

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“…They provide an excellent diagnosis of the physical conditions and processes in the regions where they reside. Progress in this field called astrochemistry is mainly driven by observations from various single-dish and interferometers at millimeter/sub-millimeter wavelengths along with space telescopes at mid-and far-infrared wavelengths (e.g., van Dishoeck 2017).…”

Section: Introductionmentioning

confidence: 99%

Chemical Diversity in Three Massive Young Stellar Objects Associated with 6.7 GHz CH₃OH Masers

Taniguchi

Saito

Majumdar

et al. 2018

ApJ

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We have carried out observations in the 42−46 and 82−103 GHz bands with the Nobeyama 45-m radio telescope, and in the 338.2−339.2 and 348.45−349.45 GHz bands with the ASTE 10-m telescope toward three high-mass star-forming regions containing massive young stellar objects (MYSOs), G12.89+0.49, G16.86−2.16, and G28.28−0.36. We have detected HC 3 N including its 13 C and D isotopologues, CH 3 OH, CH 3 CCH, and several complex organic molecules (COMs). Combining our previous results of HC 5 N in these sources, we compare the N (HC 5 N)/N (CH 3 OH) ratios in the three observed sources. The ratio in G28.28−0.36 is derived to be 0.091 +0.109 −0.039 , which is higher than that in G12.89+0.49 by one order of magnitude, and that in G16.86−2.16 by a factor of ∼ 5. We investigate the relationship between the N (HC 5 N)/N (CH 3 OH) ratio and the N (CH 3 CCH)/N (CH 3 OH) ratio. The relationships of the two column density ratios in G28.28−0.36 and G16.86−2.16 are similar to each other, while HC 5 N is less abundant when compared to CH 3 CCH in G12.89+0.49. These results imply a chemical diversity in the lukewarm (T ∼ 20 − 30 K) envelope around MYSOs. Besides, several spectral lines from complex organic molecules, including very-high-excitation energy lines, have been detected toward G12.89+0.49, while the line density is significantly low in G28.28−0.36. These results suggest that organic-poor MYSOs are surrounded by a carbon-chain-rich lukewarm envelope (G28.28−0.36), while organic-rich MYSOs, namely hot cores, are surrounded by a CH 3 OH-rich lukewarm envelope (G12.89+0.49 and G16.86−2.16).

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“…The chemical rate constants are taken primarily from the UMIST2012 database (McElroy et al 2013), but photorates are calculated using the local radiation field and cross sections from the Leiden database (van Dishoeck et al 2008) and reactions of excited H 2 ). In the screening, we restrict ourselves to the small chemical network with 100 species and 1299 reactions described by Kamp et al (2017).…”

Section: Nomentioning

confidence: 99%

“…Comparing the line ratio [C i]/CO J=3-2 with models of a 1D spherical grid of the photodissociation region can give us an estimation of the total mass and density of the region close to the central core. Other examples are interferometric measurements of CO submm lines in protoplanetary disks that yield the radial extent of the molecular gas disk (Isella et al 2007), and CN lines that can probe the vertical structure (e.g., flaring and UV penetration) of planetforming disks (Cazzoletti et al 2018;van Zadelhoff et al 2003).…”

Section: Introductionmentioning

confidence: 99%

The role of atom tunneling in gas-phase reactions in planet-forming disks

Meisner

Kamp

Thi

et al. 2019

A&A

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Context. Gas-phase chemical reactions of simple molecules have been recently revised to include atom tunneling at very low temperatures. This paper investigates the impact of the increased reaction rate constant due to tunneling effects on planet-forming disks. Aims. Our aim is to quantify the astrophysical implications of atom tunneling for simple molecules that are frequently used to infer disk structure information or to define the initial conditions for planet (atmosphere) formation. Methods. We quantify the tunneling effect on reaction rate constants by using H 2 + OH → H 2 O + H as a scholarly example in comparison to previous UMIST2012 rate constants. In a chemical network with 1299 reactions, we identify all chemical reactions that could show tunneling effects. We devise a simple formulation of reaction rate constants that overestimates tunneling and screen a standard T Tauri disk model for changes in species abundances. For those reactions found to be relevant, we find values of the most recent literature for the rate constants including tunneling and compare the resulting disk chemistry to the standard disk model(s), a T Tauri and a Herbig disk. Results. The rate constants in the UMIST2012 database in many cases already capture tunneling effects implicitly, as seen in the curvature of the Arrhenius plots of some reactions at low temperature. A rigorous screening procedure identified three neutral-neutral reactions where atom tunneling could change simple molecule abundances. However, by adopting recent values of the rate constants of these reactions and due to the layered structure of planet-forming disks, the effects are limited to a small region between the ion-molecule dominated regime and the ice reservoirs where cold (< 250 K) neutral-neutral chemistry dominates. Abundances of water close to the midplane snowline can increase by a factor of two at most compared to previous results with UMIST2012 rates. Observables from the disk surface, such as high excitation (> 500 K) water line fluxes, decrease by 60% at most when tunneling effects are explicitly excluded. On the other hand, disk midplane quantities relevant for planet formation such as the C-to-O ratio and also the ice-to-rock ratio are clearly affected by these gas-phase tunneling effects.

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Molecular Photodissociation

Cited by 13 publications

References 74 publications

Detection of HOCO+ in the protostar IRAS 16293−2422

Detection of HOCO+ in the protostar IRAS 16293−2422

Chemical Diversity in Three Massive Young Stellar Objects Associated with 6.7 GHz CH₃OH Masers

The role of atom tunneling in gas-phase reactions in planet-forming disks

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Molecular Photodissociation

Cited by 13 publications

References 74 publications

Detection of HOCO+ in the protostar IRAS 16293−2422

Detection of HOCO+ in the protostar IRAS 16293−2422

Chemical Diversity in Three Massive Young Stellar Objects Associated with 6.7 GHz CH3OH Masers

The role of atom tunneling in gas-phase reactions in planet-forming disks

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Chemical Diversity in Three Massive Young Stellar Objects Associated with 6.7 GHz CH₃OH Masers