A kinetic study of the N(2D) + C2H4 reaction at low temperature

Hickson, Kevin M.; Loison, Jean‐Christophe; Dobrijévic, M.

doi:10.1039/d0cp02083d

Cited by 10 publications

(25 citation statements)

References 68 publications

(147 reference statements)

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“…The kinetics of a few other N( 2 D) reactions were also investigated at room temperature or slightly lower temperature ( T ), but these were outside the range of relevance for Titan. The situation has recently changed as new results on the low- T kinetics for the reactions with CH 4 , C 2 H 6 , C 3 H 8 , C 2 H 2 , and C 2 H 4 have been finally obtained in a range of temperatures encompassing those of relevance for Titan by means of the reaction kinetics in uniform supersonic flow (CRESU) technique. − In addition to that, a systematic investigation of N( 2 D) reactions with simple hydrocarbons was undertaken by means of the crossed molecular beam (CMB) technique with mass-spectrometric detection by some of the present authors. CMB results have always been complemented by electronic structure calculations of the relevant stationary points of the underlying potential energy surface (PES) and statistical (Rice-Ramsperger-Kassel-Marcus) calculations of the branching fractions.…”

Section: Introductionmentioning

confidence: 99%

The Reaction N(²D) + CH₃CCH (Methylacetylene): A Combined Crossed Molecular Beams and Theoretical Investigation and Implications for the Atmosphere of Titan

et al. 2021

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The reaction of excited nitrogen atoms N( 2 D) with CH 3 CCH (methylacetylene) was investigated under single-collision conditions by the crossed molecular beams (CMB) scattering method with mass spectrometric detection and time-of-flight analysis at the collision energy ( E c ) of 31.0 kJ/mol. Synergistic electronic structure calculations of the doublet potential energy surface (PES) were performed to assist the interpretation of the experimental results and characterize the overall reaction micromechanism. Theoretically, the reaction is found to proceed via a barrierless addition of N( 2 D) to the carbon–carbon triple bond of CH 3 CCH and an insertion of N( 2 D) into the CH bond of the methyl group, followed by the formation of cyclic and linear intermediates that can undergo H, CH 3 , and C 2 H elimination or isomerize to other intermediates before unimolecularly decaying to a variety of products. Kinetic calculations for addition and insertion mechanisms and statistical (Rice-Ramsperger-Kassel-Marcus) computations of product branching fractions (BFs) on the theoretical PES were performed at different values of total energy, including the one corresponding to the temperature (175 K) of Titan’s stratosphere and that of the CMB experiment. Up to 14 competing product channels were statistically predicted, with the main ones, at E c = 31.0 kJ/mol, being the formation of CH 2 NH (methanimine) + C 2 H (ethylidyne) (BF = 0.41), c -C(N)CH + CH 3 (BF = 0.32), CH 2 CHCN (acrylonitrile) + H (BF = 0.12), and c -CH 2 C(N)CH + H (BF = 0.04). Of the 14 possible channels, seven correspond to H displacement channels of different exothermicity, for a total H channel BF of ∼0.25 at E c = 31.0 kJ/mol. Experimentally, dynamical information could only be obtained about the overall H channels. In particular, the experiment corroborates the formation of acrylonitrile + H, which is the most exothermic of all 14 reaction channels and is theoretically calculated to be the dominant H-forming channel (BF = 0.12). The products containing a novel C–N bond could be potential precursors to form other nitriles (C 2 N 2 , C 3 N) or more complex organic species containing N atoms in planetary atmospheres, such as those of Titan and Pluto. Overall, the results are expected to have a potentially significant impact on the understanding of the gas-phase chemistry of Titan’s atmosphere and the modeling of that atmosphere.

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Section: Introductionmentioning

confidence: 99%

The Reaction N(²D) + CH₃CCH (Methylacetylene): A Combined Crossed Molecular Beams and Theoretical Investigation and Implications for the Atmosphere of Titan

et al. 2021

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“…Capitalizing on the similarities between the major constituents of Triton's and Titan's atmospheres, we used the chemical scheme of Titan's atmosphere presented in Dobrijevic et al (2016) as a basis for our work. This chemical scheme was updated in Loison et al (2019), Nuñez-Reyes et al (2019a and Hickson et al (2020). The number of reactions and atmospheric species used in this scheme is presented in Table 2.…”

Section: Baseline Chemical Schemementioning

confidence: 99%

“…This leads to a high abundance of ionized atomic carbon which becomes the main ion above 175 km; this comprises an important difference with regard to the atmosphere of Titan. Once the new reactions to be included in the network were identified, the rate constants and branching ratios were chosen mainly from literature searches (e.g., Husain & Kirsch (1971) for the new critical reaction C + N 2 or Anicich (2003) for the C + reactions). When no study existed on this aspect, we followed the same methodology as in our previous studies on Titan's chemistry (Hébrard et al 2012;Loison et al 2015).…”

Section: Update Of the Chemical Schemementioning

confidence: 99%

“…Significant improvements to the modeling of the photochemistry of Titan's atmosphere have been made thanks to the Cassini-Huygens data, particularly with regard to the determination of the chemical scheme. A lot of models of this atmosphere have been developed and refined, and they are now quite robust (e.g., Dobrijevic et al 2016;Loison et al 2019;Nuñez-Reyes et al 2019a,b;Hickson et al 2020;Vuitton et al 2019). These models can be used as a starting point for the development of a new photochemical model of Triton's atmosphere, since it is composed of N 2 and CH 4 , which happen to be also the main constituents of Titan's atmosphere.…”

Section: Introductionmentioning

confidence: 99%

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A photochemical model of Triton’s atmosphere paired with an uncertainty propagation study

Benne

Dobrijévic

Cavalié

et al. 2022

A&A

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Context. The largest satellite of Neptune, Triton, is a likely Kuiper Belt object captured by the planet. It has a tenuous nitrogen atmosphere, similar to that of Pluto, and it may be an ocean world. The Neptunian system has only been visited once: by Voyager 2 in 1989. Over the past few years, the demand for a new mission to the ice giants and their systems has risen. Thus, a theoretical basis upon which to prepare for such a mission is needed. Aims. We aim to develop a photochemical model of Triton's atmosphere with an up-to-date chemical scheme, as previous photochemical models date back to the post-flyby years. This purpose is to achieve a better understanding of the mechanisms governing Triton's atmospheric chemistry and to highlight the critical parameters that have a significant impact on the atmospheric composition. We also study the model uncertainties to find what chemical studies are necessary to improve the modeling of Triton's atmosphere. Methods. We used a model of Titan's atmosphere and tailored it to Triton's conditions. We first used Titan's chemical scheme before updating it to better model Triton's atmospheric conditions. Once the nominal results were obtained, we studied the model uncertainties with a Monte Carlo procedure, considering the reaction rates as random variables. Finally, we performed global sensitivity analyses to identify the reactions responsible for model uncertainties.Results. With the nominal results, we determined the composition of Triton's atmosphere and studied the production and loss processes for the main atmospheric species. We highlighted key chemical reactions that are most important for the overall chemistry. We also identified some key parameters that have a significant impact on the results. The uncertainties are high for most of the main atmospheric species since the atmospheric temperature is very low. We identified key uncertainty reactions that have the greatest impact on the result uncertainties. These reactions must be studied as a priority in order to improve the significance of our results by finding ways of lowering these uncertainties.

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“…A lot of models of this atmosphere were developed and refined, and are now quite robust (e.g. Dobrijevic et al, 2016;Loison et al, 2019;Nuñez-Reyes et al, 2019a,b;Hickson et al, 2020;Vuitton et al, 2019). They can be used as a starting point for the development of a new photochemical model of Triton's atmosphere since it is composed of N 2 and CH 4 , which happen to be also the main constituents of Titan's atmosphere.…”

Section: Introductionmentioning

confidence: 99%

A photochemical model of Triton's atmosphere with an uncertainty propagation study

Benne

Dobrijévic

Cavalié

et al. 2022

Preprint

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Introduction Triton is the biggest satellite of Neptune. It was only visited by Voyager 2 in 1989. During this mission, the surface temperature was found to be only 38 K and the surface pressure 16 bar. It has a tenuous nitrogen atmosphere similar to the one of Pluto. This atmosphere was studied through stellar occultations and airglow observations, revealing traces of CH4 near the surface and also the presence of atomic nitrogen and hydrogen (Broadfoot et al. 1989). Radio observations pointed out the presence of a surprisingly dense ionosphere (Tyler and al. 1989).&#160; Strobel et al. (1990), Stevens et al. (1992) and Krasnopolsky and Cruikshank (1995) showed the consideration of electronic precipitation from Neptune&#8217;s magnetosphere was critical to explain the observed electronic number densities. At this distance from the Sun, the interplanetary radiation flux is also not negligible, particularly at Lyman-&#160;where it is comparable to the solar one (Broadfoot et al. 1989). Photochemical models of Triton&#8217;s atmosphere are few and were published following the Voyager flyby (Krasnopolsky et al. 1993, Krasnopolsky and Cruikshank 1995, Strobel and Summers 1995). Thus, we have developed a new photochemical model of this atmosphere with an up-to-date chemical scheme in order to prepare a potential mission to the Neptunian system. The photochemical model and methodology As the atmosphere of Triton is mostly N2 with traces of CH4, it recalls the one of Titan. Capitalizing on these similarities, we used a photochemical model of Titan&#8217;s atmosphere (Dobrijevic et al. 2016) with the chemical scheme of Hickson et al. (2020) and adapted it to Triton. To do this, we changed the critical input parameters, using data from Strobel and Zhu (2017), and updated the chemical scheme. This led us to add new atmospheric species and consider new chemical reactions. We also added the interplanetary flux and the precipitation of magnetospheric electrons. But as Triton&#8217;s atmospheric conditions are extreme, we expected large uncertainties on our results. Thus, we first computed the nominal composition of the atmosphere and then took into account the uncertainties on chemical reaction rates by using a Monte-Carlo procedure. These results were then treated through a sensitivity analysis to see how these uncertainties propagate in the model. We also added a water flux at the top of the atmosphere and used an electron transport code to better model the interaction between Triton and Neptune&#8217;s magnetosphere along its orbit. Results With the nominal results, we identify critical parameters having a significant influence on the results, such as the eddy diffusion coefficient, magnetospheric electrons or the solar flux. In addition, we highlight the main production and loss processes for the main atmospheric species. The two dominant processes are N2 ionization and dissociation by solar radiation and magnetospheric electrons, which influence the overall chemistry, and methane photolysis, that governs the chemistry in the lower atmosphere where the absorption of the Lyman-&#160;radiation is maximum. Nitrogen chemistry leads to the production of atomic nitrogen, N2+ and N+ that appear in several important reactions while methane photolysis is a source of H, H2, radicals and hydrocarbons. Due to the low temperature near the surface, these hydrocarbons condense and form hazes that were observed by Voyager. The results of the Monte-Carlo procedure show that we have indeed large uncertainties for most of the main atmospheric species. We also observe epistemic bimodalities in the abundance distribution of some species. These uncertainties rise from the lack of knowledge about reaction rates at temperatures typical of Triton&#8217;s atmosphere, which leads to large uncertainty factors on reaction rates. With the sensitivity analysis, we identify key reactions that contribute the most to the model&#8217;s uncertainties. These reactions need to be studied in priority in order to decrease the uncertainties on the results and remove any epistemic bimodalities, thus improving the significance of photochemical results. &#160; References [1] Broadfoot, A. L., S. K. Atreya, J. L. Bertaux, J. E. Blamont, A. J. Dessler, et al. &#8220;Ultraviolet Spectrometer Observations of Neptune and Triton.&#8221; Science 246, no. 4936 (December 15, 1989): 1459&#8211;66. https://doi.org/10.1126/science.246.4936.1459. [2] Tyler, G. L., D. N. Sweetnam, J. D. Anderson, S. E. Borutzki, J. K. Campbell, et al. &#8220;Voyager Radio Science Observations of Neptune and Triton.&#8221; Science 246, no. 4936 (December 15, 1989): 1466&#8211;73. https://doi.org/10.1126/science.246.4936.1466. [3] Strobel, Darrell F., Andrew F. Cheng, Michael E. Summers, and Douglas J. Strickland. &#8220;Magnetospheric Interaction with Triton&#8217;s Ionosphere.&#8221; Geophysical Research Letters 17, no. 10 (1990): 1661&#8211;64. https://doi.org/10.1029/GL017i010p01661. [4] Stevens, Michael H., Darrell F. Strobel, Michael E. Summers, and Roger V. Yelle. &#8220;On the Thermal Structure of Triton&#8217;s Thermosphere.&#8221; Geophysical Research Letters 19, no. 7 (April 3, 1992): 669&#8211;72. https://doi.org/10.1029/92GL00651. [5] Krasnopolsky, Vladimir A., and Dale P. Cruikshank. &#8220;Photochemistry of Triton&#8217;s Atmosphere and Ionosphere.&#8221; Journal of Geophysical Research 100, no. E10 (1995): 21271. https://doi.org/10.1029/95JE01904. [6] Krasnopolsky, V. A., B. R. Sandel, F. Herbert, and R. J. Vervack. &#8220;Temperature, N2, and N Density Profiles of Triton&#8217;s Atmosphere - Observations and Model.&#8221; Journal of Geophysical Research 98 (February 1, 1993): 3065&#8211;78. https://doi.org/10.1029/92JE02680.

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A kinetic study of the N(²D) + C₂H₄ reaction at low temperature

Abstract:
The barrierless N(²D) + C₂H₄ reaction is shown to be much more important to Titan's atmospheric chemistry than previously thought.

Cited by 10 publications

References 68 publications

The Reaction N(²D) + CH₃CCH (Methylacetylene): A Combined Crossed Molecular Beams and Theoretical Investigation and Implications for the Atmosphere of Titan

The Reaction N(²D) + CH₃CCH (Methylacetylene): A Combined Crossed Molecular Beams and Theoretical Investigation and Implications for the Atmosphere of Titan

A photochemical model of Triton’s atmosphere paired with an uncertainty propagation study

A photochemical model of Triton's atmosphere with an uncertainty propagation study

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A kinetic study of the N(2D) + C2H4 reaction at low temperature

Abstract: The barrierless N(2D) + C2H4 reaction is shown to be much more important to Titan's atmospheric chemistry than previously thought.

Cited by 10 publications

References 68 publications

The Reaction N(2D) + CH3CCH (Methylacetylene): A Combined Crossed Molecular Beams and Theoretical Investigation and Implications for the Atmosphere of Titan

The Reaction N(2D) + CH3CCH (Methylacetylene): A Combined Crossed Molecular Beams and Theoretical Investigation and Implications for the Atmosphere of Titan

A photochemical model of Triton’s atmosphere paired with an uncertainty propagation study

A photochemical model of Triton's atmosphere with an uncertainty propagation study

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Product

Resources

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A kinetic study of the N(²D) + C₂H₄ reaction at low temperature

Abstract:
The barrierless N(²D) + C₂H₄ reaction is shown to be much more important to Titan's atmospheric chemistry than previously thought.

The Reaction N(²D) + CH₃CCH (Methylacetylene): A Combined Crossed Molecular Beams and Theoretical Investigation and Implications for the Atmosphere of Titan

The Reaction N(²D) + CH₃CCH (Methylacetylene): A Combined Crossed Molecular Beams and Theoretical Investigation and Implications for the Atmosphere of Titan