A study of the temperature dependences of the N2+ + N2 → N4+ and O2+ + O2 → O4+ association reactions using the selected-ion flow-tube and drift-tube techniques

The three-body ion/molecule association reactions N₂⁺ + N₂ + He →$\text{k}{}_1$ N₄⁺ + He and O₂⁺ + O₂ + He →$\text{k}{}_1$ O₄⁺ + He have been studied in a variable-temperature selected-ion flow tube (SIFT) and a variable-temperature ion drift tube (DT). The rate coefficients k₁ and k₂ were determined using both apparatuses over uniquely wide temperature ranges, i.e., 45–520 K for k₁ and 48–200 K for k₂. Accurate measurements of k₂ at higher temperatures could not be made because of thermal break-up of the weakly bonded O₄⁺ ion. The magnitudes and temperature dependences of k₁ and k₂ determined in the SIFT and DT experiments are in very good agreement, and can be represented by the analytical expressions k₁ = 1.8 × 10⁻²⁹(300/T)^2.3±0.2 cm⁶ s⁻¹k₂ = 5.5 × 10⁻³¹(300/T)^2.7±0.3 cm⁶ s⁻¹ However, noticeable deviations from these power-law dependences occur at the lowest temperatures. The results are compared with those obtained from previous studies of these reactions and for the analogous association reactions involving N₂ and O₂ third bodies.