Electron-driven reactivity of molecular cations in cold plasmas

Electron impact recombination, (ro-) vibrational-, electronic- and dissociative excitation of molecular cations are at the heart of the molecular reactivity in the cold ionized media [1], being major charged molecule destruction reactions and producing often atomic species in metastable states, inaccessible through optical excitations. They involve superexcited molecular states undergoing predissociation and autoionization, having a strong resonant character. They are subject to beyond-Born-Oppenheimer approximation within the quasi-diabatic representation, and they require special treatments due to the superposition of many continua and infinite series of Rydberg states.

The methods based on the Multichannel Quantum Defect Theory (MQDT) [1,2] are the most suitable approaches for these processes, capable of accounting for the strong mixing between ionization and dissociative channels, open - direct mechanism - and closed - indirect mechanism, via capture into prominent Rydberg resonances correlating to the ground and excited ionic states, and the rotational effects.

Some of these features, characterizing the extreme (very low and very high) energies of the incident electron will be outlined in the invited talk of I. F. Schneider at this meeting [3], I will focus on the low and intermediate energy range, where core-excited bound resonances are prominent, for SH⁺ [4], N₂⁺ [5], NS⁺ [6], etc., comparisons with other existing theoretical and experimental results being displayed. Advancement in the theoretical treatment - as the inclusion of new dissociative pathways for noble gas hydrides, the isotopic effects for polyatomic systems like N₂H⁺ [7], C₂H⁺, etc. - will also be presented.