Interstellar ices as witnesses of star formation: selective deuteration of water and organic molecules unveiled

Abstract

Observations of star forming environments revealed that the abundances of some deuterated interstellar molecules are markedly larger than the cosmic D/H ratio of 10-5. Possible reasons for this pointed to grain surface chemistry. How- ever, organic molecules and water, which are both ice constituents, do not enjoy the same deuteration. For example, deuterated formaldehyde is very abundant in comets and star forming regions, while deuterated water rarely is. In this article, we explain this selective deuteration by following the formation of ices (using the rate equation method) in translucent clouds, as well as their evolu- tion as the cloud collapses to form a star. Ices start with the deposition of gas phase CO and O onto dust grains. While reaction of oxygen with atoms (H or D) or molecules (H2) yields H2O (HDO), CO only reacts with atoms (H and D) to form H2CO (HDCO, D2CO). As a result, the deuteration of formaldehyde is sensitive to the gas D/H ratio as the cloud undergoes gravitational collapse, while the deuteration of water strongly depends on the dust temperature at the time of ice formation. These results reproduce well the deuterium fractionation of formaldehyde observed in comets and star forming regions and can explain the wide spread of deuterium fractionation of water observed in these environments.

4 pages, 3 figures, Accepted in ApJ letter; Astrophysical Journal LET26536R1 2011

References in corpus (8)

• Simulation of the Formation and Morphology of Ice Mantles on Interstellar Grains
• First detection of triply-deuterated methanol
• The importance of the ortho:para H2 ratio for the deuteration of molecules during pre-protostellar collapse
• HD and H2 formation in low-metallicity dusty gas clouds at high redshift
• Ices in the Quiescent IC 5146 Dense Cloud
• Water deuterium fractionation in the low-mass protostar NGC1333-IRAS2A
• The HDO/H2O ratio in gas in the inner regions of a low-mass protostar
• Star formation in the vicinity of the IC 348 cluster

Cited by in corpus (50)

• Our astrochemical heritage
• The ALMA Protostellar Interferometric Line Survey (PILS): First results from an unbiased submillimeter wavelength line survey of the Class 0 protostellar binary IRAS 16293-2422 with ALMA
• Astrochemistry and compositions of planetary systems
• The ALMA-PILS survey: Isotopic composition of oxygen-containing complex organic molecules toward IRAS 16293-2422B
• Cometary Chemistry and the Origin of Icy Solar System Bodies, the view after Rosetta
• Water in star-forming regions (WISH): Physics and chemistry from clouds to disks as probed by Herschel spectroscopy
• A study of deuterated water in the low-mass protostar IRAS16293-2422
• From Prestellar to Protostellar Cores II. Time Dependence and Deuterium Fractionation
• Multilayer formation and evaporation of deuterated ices in prestellar and protostellar cores
• Water Formation through a Quantum Tunneling Surface Reaction, OH + H2, at 10 K
• New extended deuterium fractionation model: assessment at dense ISM conditions and sensitivity analysis
• Chemo-dynamical deuterium fractionation in the early solar nebula: The origin of water on Earth and in asteroids and comets
• Formaldehyde and methanol deuteration in protostars: fossiles from a past fast high density pre-collapse phase
• Water ice deuteration: a tracer of the chemical history of protostars
• Water deuteration and ortho-to-para nuclear spin ratio of H2 in molecular clouds formed via the accumulation of HI gas
• Reconstructing the history of water ice formation from HDO/H2O and D2O/HDO ratios in protostellar cores
• HD depletion in starless cores
• Water delivery from cores to disks: deuteration as a probe of the prestellar inheritance of H2O
• Interstellar detection of c-C3D2
• Nitrogen and hydrogen fractionation in high-mass star forming cores from observations of HCN and HNC
• Deuterated water in the solar-type protostars NGC 1333 IRAS 4A and IRAS 4B
• High D${}_2$O/HDO ratio in the inner regions of the low-mass protostar NGC1333 IRAS2A
• ALMA observations of water deuteration: A physical diagnostic of the formation of protostars
• Interferometric observations of warm deuterated methanol in the inner regions of low-mass protostars
• Chemical modeling of water deuteration in IRAS16293-2422
• Water deuterium fractionation in the high-mass star-forming region G34.26+0.15 based on Herschel/HIFI data
• Photodesorption of H2O, HDO, and D2O ice and its impact on fractionation
• Water deuterium fractionation in the inner regions of two solar type protostars
• Hydrogen isotope exchanges between water and methanol in interstellar ices
• Heavy water stratification in a low-mass protostar
• Neural-Network Assisted Study of Nitrogen Atom Dynamics on Amorphous Solid Water. I. Adsorption & Desorption
• On the relevance of the H2 + O reaction pathway for the surface formation of interstellar water - A combined experimental and modeling study
• JWST detections of amorphous and crystalline HDO ice toward massive protostars
• Successive deuteration in low-mass star-forming regions: the case of D${}_2$-methanol (CHD${}_2$OH) in IRAS 16293-2422
• Sulphur-rich cold gas around the hot core precursor G328.2551-0.5321. An APEX unbiased spectral survey of the 2 mm, 1.2 mm, and 0.8 mm atmospheric windows
• The abundance of C18O and HDO in the envelope and hot core of the intermediate mass protostar NGC 7129 FIRS 2
• A Centimeter-wave Study of Methanol and Ammonia Isotopologues in Sgr B2(N): Physical and chemical differentiation between two hot cores
• Deuterium chemistry of dense gas in the vicinity of low-mass and massive star forming regions
• Tracing the atomic nitrogen abundance in star-forming regions with ammonia deuteration
• Enhanced formation of interstellar complex organic molecules on carbon monoxide ice
• The submillimeter spectrum of deuterated glycolaldehydes
• Radial molecular abundances and gas cooling in starless cores
• Deuterated Formaldehyde in the low mass protostar HH212
• The effect of multilayer ice chemistry on gas-phase deuteration in starless cores
• Detection of a dense clump in a filament interacting with W51e2
• Modeling the processing of interstellar ices by energetic particles
• Analysis of Low Excitation HDO Transitions Toward the High-Mass Star-forming Regions G34.26+0.15, W51e${}_1$/e${}_2$, and W49N
• Isotopic fractionation in interstellar molecules
• Gas phase Elemental abundances in Molecular cloudS (GEMS). IX. Deuterated compounds of H2S in starless cores
• The distribution of deuterated formaldehyde within Orion-KL