WATER FORMATION THROUGH A QUANTUM TUNNELING SURFACE REACTION, OH + H<sub>2</sub>, AT 10 K

Oba, Yasuhiro; Watanabe, Naoki; Hama, Tetsuya; Kuwahata, Kazuaki; Hidaka, H.; Kouchi, Akira

doi:10.1088/0004-637x/749/1/67

Cited by 108 publications

(147 citation statements)

References 73 publications

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“…Water formation has been extensively studied in the solid phase over the past decade. [47][48][49][51][52][53][54][55][56] Fig. 1 and 2 show that NH 2 OH and H 2 O are the final products of the hydrogenation of NO 2 .…”

Section: Discussionmentioning

confidence: 98%

Solid state chemistry of nitrogen oxides – Part II: surface consumption of NO₂

Ioppolo

Fedoseev

Minissale

et al. 2014

Phys. Chem. Chem. Phys.

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Section: Discussionmentioning

confidence: 98%

Solid state chemistry of nitrogen oxides – Part II: surface consumption of NO₂

Ioppolo

Fedoseev

Minissale

et al. 2014

Phys. Chem. Chem. Phys.

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“…Oba et al (2012) claim to find no evidence for this reaction to proceed at low temperature. However, because of the difficulty to carry out laboratory experiments with atomic oxygen, more experiments are needed to confirm the Oba et al result.…”

Section: The Hdo * Abundancementioning

confidence: 94%

HD depletion in starless cores

Sipilä

Caselli

Harju

2013

A&A

102

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Aims. We aim to investigate the abundances of light deuterium-bearing species such as HD, H 2 D + , and D 2 H + in a gas-grain chemical model that includes an extensive description of deuterium and spin-state chemistry, in physical conditions appropriate to the very centers of starless cores. Methods. We combined a gas-grain chemical model with radiative transfer calculations to simulate density and temperature structure in starless cores. The chemical model includes new reaction sets for both gas phase and grain surface chemistry, including deuterated forms of species with up to four atoms and the spin states of the light species H 2 , H + 2 , and H + 3 and their deuterated forms. Results. We find that in the dense and cold environments attributed to the centers of starless cores, HD eventually depletes from the gas phase because deuterium is efficiently incorporated into grain-surface HDO, resulting in inefficient HD production on grains for advanced core ages. HD depletion has consequences not only on the abundances of, e.g., H 2 D + and D 2 H + , whose production depends on the abundance of HD, but also on the spin state abundance ratios of the various light species, when compared with the complete depletion model where heavy elements do not influence the chemistry. Conclusions. While the eventual HD depletion leads to the disappearance of light deuterium-bearing species from the gas phase on a relatively short timescale at high density, we find that at late stages of core evolution, the abundances of H 2 D + and D 2 H + increase toward the core edge, and the distributions become extended. The HD depletion timescale increases if less oxygen is initially present in the gas phase, owing to chemical interaction between the gas and the dust preceding the starless core phase. Our results are greatly affected if H 2 is allowed to tunnel on grain surfaces, and therefore more experimental data is needed not only on tunneling but also on the O + H 2 surface reaction in particular.

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“…These pathways include reactions with activation energy barriers, and thus proceed through quantum tunneling (Oba et al 2012(Oba et al , 2014. The barrier-mediated reactions favor hydrogenation over deuteration, because deuterium is twice heavier than hydrogen (Oba et al 2014).…”

Section: Scenariomentioning

confidence: 99%

Reconstructing the history of water ice formation from HDO/H₂O and D₂O/HDO ratios in protostellar cores

Furuya

Dishoeck

Aikawa

2016

A&A

137

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Recent interferometer observations have found that the D 2 O/HDO abundance ratio is higher than that of HDO/H 2 O by about one order of magnitude in the vicinity of low-mass protostar NGC 1333-IRAS 2A, where water ice has sublimated. Previous laboratory and theoretical studies show that the D 2 O/HDO ice ratio should be lower than the HDO/H 2 O ice ratio, if HDO and D 2 O ices are formed simultaneously with H 2 O ice. In this work, we propose that the observed feature, D 2 O/HDO > HDO/H 2 O, is a natural consequence of chemical evolution in the early cold stages of low-mass star formation as follows: 1) majority of oxygen is locked up in water ice and other molecules in molecular clouds, where water deuteration is not efficient; and 2) water ice formation continues with much reduced efficiency in cold prestellar/protostellar cores, where deuteration processes are highly enhanced as a result of the drop of the ortho-para ratio of H 2 , the weaker UV radiation field, etc. Using a simple analytical model and gas-ice astrochemical simulations, which traces the evolution from the formation of molecular clouds to protostellar cores, we show that the proposed scenario can quantitatively explain the observed HDO/H 2 O and D 2 O/HDO ratios. We also find that the majority of HDO and D 2 O ices are likely formed in cold prestellar/protostellar cores rather than in molecular clouds, where the majority of H 2 O ice is formed. This work demonstrates the power of the combination of the HDO/H 2 O and D 2 O/HDO ratios as a tool to reveal the past history of water ice formation in the early cold stages of star formation, and when the enrichment of deuterium in the bulk of water occurred. Further observations are needed to explore if the relation, D 2 O/HDO > HDO/H 2 O, is common in low-mass protostellar sources.

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WATER FORMATION THROUGH A QUANTUM TUNNELING SURFACE REACTION, OH + H₂, AT 10 K

Cited by 108 publications

References 73 publications

Solid state chemistry of nitrogen oxides – Part II: surface consumption of NO₂

Solid state chemistry of nitrogen oxides – Part II: surface consumption of NO₂

HD depletion in starless cores

Reconstructing the history of water ice formation from HDO/H₂O and D₂O/HDO ratios in protostellar cores

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WATER FORMATION THROUGH A QUANTUM TUNNELING SURFACE REACTION, OH + H2, AT 10 K

Cited by 108 publications

References 73 publications

Solid state chemistry of nitrogen oxides – Part II: surface consumption of NO2

Solid state chemistry of nitrogen oxides – Part II: surface consumption of NO2

HD depletion in starless cores

Reconstructing the history of water ice formation from HDO/H2O and D2O/HDO ratios in protostellar cores

Contact Info

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Resources

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WATER FORMATION THROUGH A QUANTUM TUNNELING SURFACE REACTION, OH + H₂, AT 10 K

Solid state chemistry of nitrogen oxides – Part II: surface consumption of NO₂

Solid state chemistry of nitrogen oxides – Part II: surface consumption of NO₂

Reconstructing the history of water ice formation from HDO/H₂O and D₂O/HDO ratios in protostellar cores