Combined crossed molecular beams and computational study on the N(²D) + HCCCN(X¹Σ⁺) reaction and implications for extra-terrestrial environments

Abstract

The reaction of the nitrogen atom (N) in its first electronically excited state (²D) with cyanoacetylene (HC₃N) has been investigated under single-collision conditions by using the crossed molecular beam method with mass spectrometric detection at a collision energy of 31 kJ mol⁻¹. With the support of electronic structure calculations, we found that this reaction proceeds via the barrierless addition of the N(²D) atom to the carbon–carbon triple bond of HC₃N, followed by the formation of a cyclic intermediate adduct HC(N)CCN, which dissociates to C(N)CCN + H products or isomerises to a more stable intermediate HNCCCN by H-migration and ring-opening processes. The long-lived HNCCCN complex produces the linear ³Σ_g^– ground state dicyanocarbene (NCCCN) radical plus atomic hydrogen through a barrierless unimolecular dissociation accompanied by a negligible competitive channel forming the NCCCN radical (¹A₁) with a bent C_2v structure plus H. The main product of this neutral-neutral reaction is the ³NCCCN radical that could be a potential precursor to form other nitriles (C₂N₂, C₃N) or more complex organic species in planetary atmospheres, such as that of Titan and Pluto, in cometary comas, and in UV irradiated interstellar environments.

GRAPHICAL ABSTRACT

KEYWORDS:

• Crossed molecular beams
• electronic structure calculations
• N(²D)  reactions
• extra-terrestrial environments
• titan

Acknowledgments

The authors thank Isabelle Couturier-Tamburelli (Aix-Marseille Université-PIIM, Marseille, FR), Murthy Gudipati (JPL, USA) and Benjamin Fleury (JPL, USA) for kindly sharing their experience in synthesising and handling of HC₃N. Y. T. acknowledges financial support from the extra-[EU ERASMUS+ program (Academic Year 2019/2020)].

Disclosure statement

No potential conflict of interest was reported by the author(s).

Correction Statement

This article has been corrected with minor changes. These changes do not impact the academic content of the article.

Additional information

Funding

This work was supported by the Italian Space Agency (ASI, DC-VUM-2017-034, Grant n° 2019–3 U.O Life in Space) and by the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 811312 for the project ‘Astro-Chemical Origins’ (ACO).