Laboratory measurements of the association rate coefficients of NO+, O+2, N+, and N+2 ions with N2 and CO2 at temperatures between 100 k and 400 k

Rate coefficients for the association reactions of NO⁺ ions with N₂ and CO₂, O₂⁺ with N₂, and N⁺ and N₂⁺ with N₂ have been determined as a function of gas temperature in a laboratory experiment employing a variable-temperature drift-tube apparatus. The measured rate coefficients were fitted to power laws of the form $\text{k = C}\text{(}\text{T}\text{300}\text{)}{}^{\mathrm{x}}$ where the exponents x ranged from 2.2 to 4.3. The strong temperature dependence observed in the case of the reaction of NO⁺ with N₂ (x = 4.3) supports the thesis by Arnold et al. (1979) that the temperature variability of D-region ion densities is a result of this reaction step in the ion clustering sequence.     

Measured ion-molecule reaction rates for modelling Titan's atmosphere

Rate coefficients for several two- and three-body ion-molecule reactions involving hydrocarbons have been determined at thermal energies and above using drift tube-mass spectrometer techniques. The measured rates for clustering and breakup reactions involving CH₅⁺ and C₂H₅⁺ ions in methane are found to be strongly temperature dependent in the range from 80 to 240 K. The equilibrium constants determined for these reactions differ somewhat from those of Hiraoka and Kebarle. Rate coefficients for two-body reactions of CH₅⁺, C₂H₅⁺, N⁺, H⁺ and D⁺ ions with methane and/or ethane have been measured. The results indicate that the product yields of several of the fast ion-molecule reactions depend strongly on ion energy (temperature), and therefore previous room-temperature results may be of limited value for model calculations of Titan's atmosphere.