Experimental characterization of the energetics of low-temperature surface reactions

Henning, Thomas; Krasnokutski, Serge A.

doi:10.1038/s41550-019-0729-8

Cited by 26 publications

(22 citation statements)

References 44 publications

(54 reference statements)

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“…Most of these reactions are related to the growth of the carbon chains C n X + C → C n+1 X, where X could be H, O, N, S, or none. This is in strong contrast to numerous laboratory studies that demonstrated that C atoms can react without a barrier with almost all species present in the ice mantles (Chastaing et al 2000(Chastaing et al , 2001Kaiser & Mebel 2002;Kaiser et al 1999;Krasnokutski et al 2017aKrasnokutski et al , 2019Krasnokutski et al , 2020Shannon et al 2014;Henning & Krasnokutski 2019;Hickson et al 2016).…”

Section: Reactivity Of Carbon Atoms On Dust Grain Surfaces: Missing Pcontrasting

confidence: 72%

“…The liquid helium acts like a chemically inert dust surface because it absorbs the excess of reaction energy. The reaction C + H 2 + M → CH 2 + M was found to be fast at T = 0.37 K (Krasnokutski et al 2016;Henning & Krasnokutski 2019). This demonstrates the absence of the energy barrier in the surface reaction pathway and ensures a high reaction rate at low temperatures in the ISM.…”

Section: Introductionmentioning

confidence: 83%

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Sensitivity of gas-grain chemical models to surface reaction barriers

Simončič

Semenov

Krasnokutski

et al. 2020

A&A

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Context. The feasibility of contemporary gas-grain astrochemical models depends on the availability of accurate kinetics data, in particular, for surface processes. Aims. We study the sensitivity of gas-grain chemical models to the energy barrier Ea of the important surface reaction between some of the most abundant species: C and H2 (surface C + surface H2 → surface CH2). Methods. We used the gas-grain code ALCHEMIC to model the time-dependent chemical evolution over a 2D grid of densities (nH ∈ 103, 1012 cm−3) and temperatures (T ∈ 10, 300 K), assuming UV-dark (AV = 20 mag) and partly UV-irradiated (AV = 3 mag) conditions that are typical of the dense interstellar medium. We considered two values for the energy barrier of the surface reaction, Ea = 2500 K (as originally implemented in the networks) and Ea = 0 K (as measured in the laboratory and computed by quantum chemistry simulations). Results. We find that if the C + H2 → CH2 surface reaction is barrierless, a more rapid conversion of the surface carbon atoms into methane ice occurs. Overproduction of the CHn hydrocarbon ices affects the surface formation of more complex hydrocarbons, cyanides and nitriles, and CS-bearing species at low temperatures ≲10−15 K. The surface hydrogenation of CO and hence the synthesis of complex (organic) molecules become affected as well. As a result, important species whose abundances may change by more than a factor of two at 1 Myr include atomic carbon, small mono-carbonic (C1) and di-carbonic (C2) hydrocarbons, CO2, CN, HCN, HNC, HNCO, CS, H2CO, H2CS, CH2CO, and CH3OH (in either gas and/or ice). The abundances of key species, CO, H2O, and N2 as well as O, HCO+, N2H+, NH3, NO, and most of the S-bearing molecules, remain almost unaffected. Conclusions. Further accurate laboratory measurements and quantum chemical calculations of the surface reaction barriers will be crucial to improve the accuracy of astrochemical models.

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Section: Reactivity Of Carbon Atoms On Dust Grain Surfaces: Missing Pcontrasting

confidence: 72%

Section: Introductionmentioning

confidence: 83%

Sensitivity of gas-grain chemical models to surface reaction barriers

Simončič

Semenov

Krasnokutski

et al. 2020

A&A

View full text Add to dashboard Cite

show abstract

“…Most of these reactions are related to the growth of the carbon chains C n X + C → C n+1 X, where X could be H, O, N, S, or none. This is in strong contrast to numerous laboratory studies that demonstrated that C atoms can react without a barrier with almost all species present in the ice mantles (Chastaing et al 2000(Chastaing et al , 2001Kaiser & Mebel 2002;Kaiser et al 1999;Krasnokutski et al 2017b;Shannon et al 2014;Krasnokutski et al 2019;Henning & Krasnokutski 2019;Krasnokutski et al 2020;Hickson et al 2016).…”

Section: Reactivity Of Carbon Atoms On Dust Grain Surfacescontrasting

confidence: 66%

Sensitivity of gas-grain chemical models to surface reaction barriers: Effect from a key carbon-insertion reaction, C + H$_2$ $\rightarrow$ CH$_2$

Simončič,

Semenov,

Krasnokutski

et al. 2020

Preprint

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Context. The feasibility of contemporary gas-grain astrochemical models depends on the availability of accurate kinetics data, in particular, for surface processes. Aims. We study the sensitivity of gas-grain chemical models to the energy barrier E a of the important surface reaction between some of the most abundant species: C and H 2 (surface C + surface H 2 → surface CH 2 ). Methods. We used the gas-grain code ALCHEMIC to model the time-dependent chemical evolution over a 2D grid of densities (n H ∈ 10 3 , 10 12 cm −3 ) and temperatures (T ∈ 10, 300 K), assuming UV-dark (A V = 20 mag) and partly UV-irradiated (A V = 3 mag) conditions that are typical of the dense interstellar medium. We considered two values for the energy barrier of the surface reaction, E a = 2 500 K (as originally implemented in the networks) and E a = 0 K (as measured in the laboratory and computed by quantum chemistry simulations). Results. We find that if the C + H 2 → CH 2 surface reaction is barrierless, a more rapid conversion of the surface carbon atoms into methane ice occurs. Overproduction of the CH n hydrocarbon ices affects the surface formation of more complex hydrocarbons, cyanides and nitriles, and CS-bearing species at low temperatures 10 − 15 K. The surface hydrogenation of CO and hence the synthesis of complex (organic) molecules become affected as well. As a result, important species whose abundances may change by more than a factor of two at 1 Myr include atomic carbon, small mono-carbonic (C 1 ) and di-carbonic (C 2 ) hydrocarbons, CO 2 , CN, HCN, HNC, HNCO, CS, H 2 CO, H 2 CS, CH 2 CO, and CH 3 OH (in either gas and/or ice). The abundances of key species, CO, H 2 O, and N 2 as well as O, HCO + , N 2 H + , NH 3 , NO, and most of the S-bearing molecules, remain almost unaffected. Conclusions. Further accurate laboratory measurements and quantum chemical calculations of the surface reaction barriers will be crucial to improve the accuracy of astrochemical models.

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“…This is a reason why there is little known regarding the role and relevance of C-atom addition reactions in solid-state astrochemical processes. Recent laboratory works have demonstrated how atomic carbon can react to form simple radicals 26,27 and COMs 28 within liquid helium droplets. The present work extends this with the first ice system capable of studying C-atom chemistry reactions in interstellar ice analogs.…”

Section: Introductionmentioning

confidence: 99%