Three-body association reactions of H+ and H3+ ions in hydrogen from 135 to 300 K

Abstract

Rate coefficients for the reactions H⁺+2H₂?h₃⁺+H₂ [Reaction (1)] and H₃⁺+2H₂?H₅⁺+H₂ [Reaction (2)] have been determined at several temperatures in a drift‐tube mass spectrometer apparatus. Reaction (1) was found to have forward rate coefficients of (3.0±0.3) and (4.3±0.4) ×10⁻²⁹ cm⁶/s at a temperature of 300 K and at temperatures between 135 and 160 K, respectively. Reaction (2) was found to have forward rate coefficients of (12±2), (9.5±3), (6.2±2.0), and (4.6±1.5) ×10⁻³⁰ cm⁶/s at 156, 195, 203, and 210 K, respectively. Equilibrium constants for Reaction (2) were determined in the temperature range 176–320 K. The temperature dependence of the equilibrium constant indicates a dissociation energy of (0.35±0.03) eV for breakup of H₅⁺ into H₃⁺ and H₂.