OH+ Formation in the Low-temperature O+(4S) + H2 Reaction

Formation of OH⁺ in collisions of ground-state O⁺(⁴S) ions with normal H₂ has been studied using a variable temperature 22-pole RF ion trap. From 300 to 30 K the measured reaction rate coefficient is temperature-independent, with a small decrease toward 15 K. The recent wave packet calculation predicts a slightly steeper temperature dependence. The rate coefficients at 300 and 15 K are almost the same, (1.4 ± 0.3) × 10^-9 cm³ s^-1 and (1.3 ± 0.3) × 10^-9 cm³ s^-1, respectively. The influence of traces of the two metastable ions, O⁺(²D) and O⁺(²P), has been examined by monitoring the H⁺ products of their reactions with H₂, as well as by chemically probing them with N₂ reactant gas.