Kinetics of CO+ and CO2+ with N and O atoms

We have measured reaction rate constants for CO⁺ and CO₂⁺ reacting with N and O atoms using a selected ion flow tube apparatus equipped with a microwave discharge atom source. Experimental work was supplemented by molecular structure calculations. Calculated pathways show the sensitivity of kinetic barriers to theoretical methods and imply that high-level ab initio methods are required for accurate energetics. We report room-temperature rate constants of 1.0 ± 0.4 × 10^-11 cm³ s^-1 and 4.0 ± 1.6 × 10^-11 cm³ s^-1 for the reactions of CO⁺ with N and O atoms, respectively, and 8.0 ± 3.0 × 10^-12 cm³ s^-1 and 2.0 ± 0.8 × 10^-11 cm³ s^-1 for the reactions of CO₂⁺ with N and O atoms, respectively. The reaction of CO₂⁺ + O is observed to yield O₂⁺ exclusively. These values help resolve discrepancies in the literature and are important for modeling of the Martian atmosphere.

When electrons meet molecular ions and what happens next: dissociative recombination from interstellar molecular clouds to internal combustion engines

The interaction of matter with its environment is the driving force behind the evolution of 99% of the observed matter in the universe. The majority of the visible universe exists in a state of weak ionization, the so called fourth state of matter: plasma. Plasmas are ubiquitous, from those occurring naturally; interstellar molecular clouds, cometary comae, circumstellar shells, to those which are anthropic in origin; flames, combustion engines and fusion reactors. The evolution of these plasmas is driven by the interaction of the plasma constituents, the ions, and the electrons. One of the most important subsets of these reactions is electron-molecular ion recombination. This process is significant for two very important reasons. It is an ionization reducing reaction, removing two ionised species and producing neutral products. Furthermore, these products may themselves be reactive radical species which can then further drive the evolution of the plasma. The rate at which the electron reacts with the ion depends on many parameters, for examples the collision energy, the internal energy of the ion, and the structure of the ion itself. Measuring these properties together with the manner in which the system breaks up is therefore critical if the evolution of the environment is to be understood at all. Several techniques have been developed to study just such reactions to obtain the necessary information on the parameters. In this paper the focus will be on one the most recently developed of these, the Ion Storage Ring, together with the detection tools and techniques used to extract the necessary information from the reaction.