Electron-induced reactivity of molecular cations in low-temperature plasmas and astrochemistry*

The kinetics of electrons and of molecular cations in ionized cold media is mainly controlled by the dissociative recombination, competed by autoionization. These processes are studied theoretically using different approaches, the most effective being those based on the Multichannel Quantum Defect Theory (MQDT) [1].

I will start by showing how we use our stepwise version of the MQDT in order to compute cross sections and rate coefficients for the collision between electrons and several molecular cations present in the edge plasmas of fusion reactors. Focusing on extreme values of the energy/temperature of the electrons, this presentation is complementary to that of J. Zs. Mezei [2], devoted to intermediate values of these parameters. I will illustrate the different mechanisms for BeH⁺, BeD⁺, BeT⁺ [3] and ArH⁺ [1], insisting on the competition between dissociative recombination and dissociative excitation above the dissociative threshold of the target. 

In the case of H₂⁺, HD⁺ and D₂⁺ [4], I will focus on very low energies, of the order of the rotational/vibrational quanta, where isotopic and rotational effects are particularly strong. These latter species are relevant for the interstellar medium, as NS⁺ [5, 6] and CF⁺, for which very recent results will be also shown. In particular, CF⁺ is the object of a novel MQDT approach, developed by J. Forer and his collaborators [7].