Issue 8, 2018

The reaction of C5N with acetylene as a possible intermediate step to produce large anions in Titan's ionosphere

Abstract

A theoretical and experimental investigation of the reaction C5N + C2H2 has been carried out. This reaction is of astrophysical interest since the growth mechanism of large anions that have been detected in Titan's upper atmosphere by the Cassini plasma spectrometer are still largely unknown. The experimental studies have been performed using a tandem quadrupole mass spectrometer which allows identification of the different reaction channels and assessment of their reaction thresholds. Results of these investigations were compared with the predictions of ab initio calculations, which identified possible pathways leading to the observed products and their thermodynamical properties. These computations yielded that the majority of these products are only accessible via energy barriers situated more than 1 eV above the reactant energies. In many cases, the thresholds predicted by the ab initio calculations are in good agreement with the experimentally observed ones. For example, the chain elongation reaction leading to C7N, although being slightly exoergic, possesses an energy barrier of 1.91 eV. Therefore, the title reaction can be regarded to be somewhat unlikely to be responsible for the formation of large anions in cold environments such as interstellar medium or planetary ionospheres.

Graphical abstract: The reaction of C5N− with acetylene as a possible intermediate step to produce large anions in Titan's ionosphere

Article information

Article type
Paper
Submitted
14 Sep 2017
Accepted
06 Oct 2017
First published
06 Oct 2017

Phys. Chem. Chem. Phys., 2018,20, 5377-5388

The reaction of C5N with acetylene as a possible intermediate step to produce large anions in Titan's ionosphere

C. F. Lindén, J. Žabka, M. Polášek, I. Zymak and W. D. Geppert, Phys. Chem. Chem. Phys., 2018, 20, 5377 DOI: 10.1039/C7CP06302D

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