Of much lower abundance than neutral species in astrophysical environments, charged species play nevertheless a capital role. Often without activation barrier, reactions in the gas phase involving charged species can turn out very fast and thus govern the chemistry of these diluted media.
In the upper atmosphere of Titan, the heavy negative ions recently detected could be the origin of aerosols that produce a thick haze obscuring the surface. In interstellar clouds or planetary ionospheres, recombination is a major destruction mechanism of many molecular ions. The ionization state of these molecules in these environments depends mostly on the competition between processes.
Despite numerous theoretical studies, processes involving ions (ion-electron recombination, ion-molecule reaction, electron attachment…) remain difficult to predict satisfactorily. Two pieces of information are fundamental: the kinetics of the reaction and the nature of the products with the branching into the different channels.
In our laboratory, we investigate the kinetics of reactions and the nature of products of ion-molecule reactions over the 20 to 300 K temperature range with a dedicated CRESU chamber. Our efforts have been recently focused on the reactivity of negative ions which have been detected in the interstellar medium and in the atmosphere of Titan. In parallel, we make some measurements of ion-electron recombination with a flowing afterglow tube at room temperature.
Our research can also find some applications in aerodynamics, combustion and plasma physics.
Low temperature reaction kinetics of CN‑ + HC3N and implications for the growth of anions in Titan’s atmosphere, Ludovic Biennier; Sophie Carles; Daniel Cordier; Jean-Claude Guillemin; Sebastien D. Le Picard; Alexandre Faure, Icarus, 2014, 227, pp. 123-131, DOI