Low-Temperature Kinetic Isotope Effects in CH3OH + H → CH2OH + H2 Shed Light on the Deuteration of Methanol in Space

Cooper, April M.; Kästner, Johannes

doi:10.1021/acs.jpca.9b07013

Cited by 18 publications

(18 citation statements)

References 60 publications

(154 reference statements)

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“…Deuterium fractionation occurs primarily as a result of gas phase processes, but grain surface reactions at low temperatures (∼10 K) can further enhance the level of fractionation (Watanabe and Kouchi 2008;Fedoseev et al 2015). The degree of deuterium fractionation of formaldehyde and methanol can be enhanced by the substitution and abstraction reactions of H and D atoms at ∼10 K after their formation (Watanabe and Kouchi 2008;Taquet et al 2012;Cooper and Kästner 2019). As other examples, methylamine (CH 3 NH 2 ) and ethanol (CH 3 CH 2 OH) are also subject to the H/D substitution reactions (Oba et al 2014(Oba et al , 2016.…”

Section: Deuterium Fractionationmentioning

confidence: 99%

The Isotopic Links from Planet Forming Regions to the Solar System

Nomura¹,

Furuya²,

Cordiner³

et al. 2022

Preprint

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Isotopic ratios provide a powerful tool for understanding the origins of materials, including the volatile and refractory matter within solar system bodies. Recent high sensitivity observations of molecular isotopologues, in particular with ALMA, have brought us new information on isotopic ratios of hydrogen, carbon, nitrogen and oxygen in star and planet forming regions as well as the solar system objects. Solar system exploration missions, such as Rosetta and Cassini, have given us further new insights. Meanwhile, the recent development of sophisticated models for isotope chemistry including detailed gas-phase and grain surface reaction network has made it possible to discuss how isotope fractionation in star and planet forming regions is imprinted into the icy mantles of dust grains, preserving a record of the initial isotopic state of solar system materials. This chapter reviews recent progress in observations of molecular isotopologues in extra-solar planet forming regions, prestellar/protostellar cores and protoplanetary disks, as well as objects in our solar system -comets, meteorites, and planetary/satellite atmospheres -and discusses their connection by means of isotope chemical models.

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Section: Deuterium Fractionationmentioning

confidence: 99%

The Isotopic Links from Planet Forming Regions to the Solar System

Nomura¹,

Furuya²,

Cordiner³

et al. 2022

Preprint

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“…For instance, quantitative information on the contribution from each atom can be extracted such that kinetic isotope effects can be easily predicted and understood [26][27][28]. It has, for instance, been applied to gas-phase reactions [29][30][31], tunnelling in molecules and clusters [28,[32][33][34][35], enzymatic reactions [36], surface diffusion processes [37,38] and water formation reactions [39]. An extension of the original instanton theory has been derived which provides a semiclassical approximation to FGR rates of non-adiabatic reactions and predicts very good results for benchmark model systems [40][41][42].…”

Section: Introductionmentioning

confidence: 99%

Instanton theory for Fermi’s golden rule and beyond

Ansari

Heller

Trenins

et al. 2022

Phil. Trans. R. Soc. A.

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Instanton theory provides a semiclassical approximation for computing quantum tunnelling effects in complex molecular systems. It is typically applied to proton-transfer reactions for which the Born–Oppenheimer approximation is valid. However, many processes in physics, chemistry and biology, such as electron transfers, are non-adiabatic and are correctly described instead using Fermi’s golden rule. In this work, we discuss how instanton theory can be generalized to treat these reactions in the golden-rule limit. We then extend the theory to treat fourth-order processes such as bridge-mediated electron transfer and apply the method to simulate an electron moving through a model system of three coupled quantum dots. By comparison with benchmark quantum calculations, we demonstrate that the instanton results are much more reliable than alternative approximations based on superexchange-mediated effective coupling or a classical sequential mechanism. This article is part of the theme issue ‘Chemistry without the Born–Oppenheimer approximation’.

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“…This has been done similarly as described in Lamberts (2018). Furthermore, the rate of the reaction CH 3 OH + H → CH 2 OH + H 2 has been updated to 7.22 × 10 3 s −1 following Cooper & Kästner (2019).…”

Section: Kinetic Monte Carlo Simulationsmentioning

confidence: 99%

Methoxymethanol Formation Starting from CO-Hydrogenation

He,

Simons,

Fedoseev

et al. 2021

Preprint

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Context. Methoxymethanol (CH 3 OCH 2 OH) has been identified through gas-phase signatures in both high-and low-mass star-forming regions. Like several other C-, O-and H-containing COMs (complex organic molecules), this molecule is expected to form upon hydrogen addition and abstraction reactions in CO-rich ice through radical recombination of CO hydrogenation products. Aims. The goal of this work is to investigate experimentally and theoretically the most likely solid-state methoxymethanol reaction channel -the recombination of CH 2 OH and CH 3 O radicals -for dark interstellar cloud conditions and to compare the formation efficiency with that of other species that were shown to form along the CO-hydrogenation line. Also, an alternative hydrogenation channel starting from methyl formate has been investigated. Methods. Hydrogen atoms and CO or H 2 CO molecules are co-deposited on top of the predeposited H 2 O ice to mimic the conditions associated with the beginning of 'rapid' CO freeze-out. The formation of simple species is monitored in situ by infrared spectroscopy. Quadrupole mass spectrometry is used to analyze the gas-phase COM composition following a temperature programmed desorption. Monte Carlo simulations are used for an astrochemical model comparing the methoxymethanol formation efficiency with that of other COMs.Results. The laboratory identification of methoxymethanol is found to be challenging, in part because of diagnostic limitations, but possibly also because of low formation efficiencies. Nevertheless, unambiguous detection of newly formed methoxymethanol has been possible both in CO+H and H 2 CO+H experiments. The resulting abundance of methoxymethanol with respect to CH 3 OH is about 0.05, which is about 6 times less than the value observed toward NGC 6334I and about 3 times less than the value reported for IRAS 16293B. The results of astrochemical simulations predict a similar value for the methoxymethanol abundance with respect to CH 3 OH factors ranging between 0.06 to 0.03. Conclusions. We find that methoxymethanol is formed by co-deposition of CO and H 2 CO with H atoms through the recombination of CH 2 OH and CH 3 O radicals. In both the experimental and modeling studies, it is found that the efficiency of this channel alone is not sufficient to explain the observed abundance of methoxymethanol with respect to methanol. The rate of a proposed alternative channel, the direct hydrogenation of methyl formate, is found to be even less efficient. These results indicate an incomplete knowledge of the reaction network or the presence of alternative solid-state or gas-phase formation mechanisms.

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Low-Temperature Kinetic Isotope Effects in CH₃OH + H → CH₂OH + H₂ Shed Light on the Deuteration of Methanol in Space

Cited by 18 publications

References 60 publications

The Isotopic Links from Planet Forming Regions to the Solar System

The Isotopic Links from Planet Forming Regions to the Solar System

Instanton theory for Fermi’s golden rule and beyond

Methoxymethanol Formation Starting from CO-Hydrogenation

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