Dissociative recombination of N2H+ ions with electrons in the temperature range of 80–350 K

Shapko, Dmytro; Dohnal, Petr; Kassayová, Miroslava; Kálosi, Ábel; Rednyk, Serhiy; Roučka, Štěpán; Plašil, R.; Augustovičová, Lucie D.; Johnsen, Rainer; Špirko, V.; Glosı́k, J.

doi:10.1063/1.5128330

Cited by 7 publications

(4 citation statements)

References 79 publications

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“…We notice at this point also the crucial importance of the branching ratio of this reaction, which has been the object of several contradicting experiments. The present value is taken as 0.10, following the latest experimental value of Shapko et al (2020).…”

Section: Discussionmentioning

confidence: 99%

Sustained oscillations in interstellar chemistry models

Roueff

Bourlot

2020

A&A

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Context. Nonlinear behavior in interstellar chemical models has been recognized for 25 years now. Different mechanisms account for the possibility of multiple fixed-points at steady-state, characterized by the ionization degree of the gas. Aims. Chemical oscillations are also a natural behavior of nonlinear chemical models. We study under which conditions spontaneous sustained chemical oscillations are possible, and what kind of bifurcations lead to, or quench, the occurrence of such oscillations. Methods. The well-known ordinary differential equations (ODE) integrator VODE was used to explore initial conditions and parameter space in a gas phase chemical model of a dark interstellar cloud. Results. We recall that the time evolution of the various chemical abundances under fixed temperature conditions depends on the density over cosmic ionization rate n H /ζ ratio. We also report the occurrence of naturally sustained oscillations for a limited but welldefined range of control parameters. The period of oscillations is within the range of characteristic timescales of interstellar processes and could lead to spectacular resonances in time-dependent models. Reservoir species (C, CO, NH 3 , ...) oscillation amplitudes are generally less than a factor two. However, these amplitudes reach a factor ten to thousand for low abundance species, e.g. HCN, ND 3 , that may play a key role for diagnostic purposes. The mechanism responsible for oscillations is tightly linked to the chemistry of nitrogen, and requires long chains of reactions such as found in multi-deuteration processes.

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Section: Discussionmentioning

confidence: 99%

Sustained oscillations in interstellar chemistry models

Roueff

Bourlot

2020

A&A

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“…experimentally studied by Montaigne et al (2005) and there are no specific reasons to question this value. Nevertheless, there is only an experimental value and it can be noted that the DR of HCNH + (Adams et al 1991;Semaniak et al 2001;McLain & Adams 2009) and N 2 H + (Shapko et al 2020) vary greatly from one measurement to another. New experimental measurements of the DR of HCS + would be desirable to confirm the currently used value.…”

Section: Astrophysical Implicationsmentioning

confidence: 99%

Gas phase Elemental abundances in Molecular cloudS (GEMS)

Bulut

Roncero

Aguado

et al. 2021

A&A

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Context. Carbon monosulphide (CS) is among the most abundant gas-phase S-bearing molecules in cold dark molecular clouds. It is easily observable with several transitions in the millimeter wavelength range, and has been widely used as a tracer of the gas density in the interstellar medium in our Galaxy and external galaxies. However, chemical models fail to account for the observed CS abundances when assuming the cosmic value for the elemental abundance of sulfur. Aims. The CS+O → CO + S reaction has been proposed as a relevant CS destruction mechanism at low temperatures, and could explain the discrepancy between models and observations. Its reaction rate has been experimentally measured at temperatures of 150−400 K, but the extrapolation to lower temperatures is doubtful. Our goal is to calculate the CS+O reaction rate at temperatures <150 K which are prevailing in the interstellar medium. Methods. We performed ab initio calculations to obtain the three lowest potential energy surfaces (PES) of the CS+O system. These PESs are used to study the reaction dynamics, using several methods (classical, quantum, and semiclassical) to eventually calculate the CS + O thermal reaction rates. In order to check the accuracy of our calculations, we compare the results of our theoretical calculations for T ~ 150−400 K with those obtained in the laboratory. Results. Our detailed theoretical study on the CS+O reaction, which is in agreement with the experimental data obtained at 150–400 K, demonstrates the reliability of our approach. After a careful analysis at lower temperatures, we find that the rate constant at 10 K is negligible, below 10−15 cm3 s−1, which is consistent with the extrapolation of experimental data using the Arrhenius expression. Conclusions. We use the updated chemical network to model the sulfur chemistry in Taurus Molecular Cloud 1 (TMC 1) based on molecular abundances determined from Gas phase Elemental abundances in Molecular CloudS (GEMS) project observations. In our model, we take into account the expected decrease of the cosmic ray ionization rate, ζH2, along the cloud. The abundance of CS is still overestimated when assuming the cosmic value for the sulfur abundance.

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“…This DR has been experimentally studied by Montaigne et al (2005) and there are no specific reasons to question this value. Nevertheless, there is only an experimental value and it should be noted that the DR of HCNH + (Adams et al 1991;Semaniak et al 2001;McLain & Adams 2009) and N 2 H + (Shapko et al 2020) vary greatly from one measurement to another. New experimental measurements of the DR of HCS + would be desirable to confirm the currently used value.…”

Section: Astrophysical Implicationsmentioning

confidence: 99%

Gas-phase Elemental abundances in Molecular cloudS (GEMS) III. Unlocking the CS chemistry: the CS+O reaction

Bulut,

Roncero,

Aguado

et al. 2020

Preprint

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Context. Carbon monosulphide (CS) is among the most abundant gas-phase S-bearing molecules in cold dark molecular clouds. It is easily observable with several transitions in the millimeter wavelength range, and has been widely used as a tracer of the gas density in the interstellar medium in our Galaxy and external galaxies. However, chemical models fail to account for the observed CS abundances when assuming the cosmic value for the elemental abundance of sulfur. Aims. The CS+O → CO + S reaction has been proposed as a relevant CS destruction mechanism at low temperatures, and could explain the discrepancy between models and observations. Its reaction rate has been experimentally measured at temperatures of 150−400 K, but the extrapolation to lower temperatures is doubtful. Our goal is to calculate the CS+O reaction rate at temperatures <150 K which are prevailing in the interstellar medium. Methods. We performed ab initio calculations to obtain the three lowest potential energy surfaces (PES) of the CS +O system. These PESs are used to study the reaction dynamics, using several methods (classical, quantum, and semiclassical) to eventually calculate the CS + O thermal reaction rates. In order to check the accuracy of our calculations, we compare the results of our theoretical calculations for T∼150−400 K with those obtained in the laboratory. Results. Our detailed theoretical study on the CS+O reaction, which is in agreement with the experimental data obtained at 150-400 K, demonstrates the reliability of our approach. After a careful analysis at lower temperatures, we find that the rate constant at 10 K is negligible, below 10 −15 cm 3 s −1 , which is consistent with the extrapolation of experimental data using the Arrhenius expression. Conclusions. We use the updated chemical network to model the sulfur chemistry in Taurus Molecular Cloud 1 (TMC 1) based on molecular abundances determined from Gas phase Elemental abundances in Molecular CloudS (GEMS) project observations. In our model, we take into account the expected decrease of the cosmic ray ionization rate, ζ H 2 , along the cloud. The abundance of CS is still overestimated when assuming the cosmic value for the sulfur abundance.

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Dissociative recombination of N2H+ ions with electrons in the temperature range of 80–350 K

Cited by 7 publications

References 79 publications

Sustained oscillations in interstellar chemistry models

Sustained oscillations in interstellar chemistry models

Gas phase Elemental abundances in Molecular cloudS (GEMS)

Gas-phase Elemental abundances in Molecular cloudS (GEMS) III. Unlocking the CS chemistry: the CS+O reaction

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