The dissociative recombination rate coefficients of H⁺₃, HN⁺₂, and HCO⁺

The dissociative recombination rate coefficients for H⁺₃, HN⁺₂, and HCO⁺ are determined at 110, 210, and 273 K by monitoring the decay of the infrared absorption signals as a function of time. The rate coefficients are 1.8, 7.0, and 3.1 in units of 10⁻⁷ cm³ s⁻¹ for H⁺₃, HN⁺₂, and HCO⁺, respectively, at 273 K. These values agree very well with those obtained using the stationary afterglow or the merged beam techniques, but the values for H⁺₃ disagree with that obtained by Smith and co‐workers (≤2×10⁻⁸ cm³ s⁻¹) using the flowing afterglow/Langmuir probe method. The rate coefficients for H⁺₃ and HCO⁺ disagree with theory which has predicted very slow dissociative recombinations in the lower vibrational states. The temperature dependences obtained here, although the temperature range is rather limited, are consistent with those obtained previously using the stationary afterglow (for H⁺₃ and HCO⁺) and the merged beam (for HN⁺₂) techniques. The measurements are extended to several vibration–rotation levels and no significant rotation dependence of the rate coefficients is observed. It has also been found that the ions investigated here can be equally abundant at ice temperature as at liquid nitrogen temperature.