ICR studies of some hydrogen atom abstraction reactions: X+ + H2 → XH+ + H

Abstract

Ion cyclotron resonance methods are used to identify and to measure the rate constants for the abstraction of a hydrogen atom from H₂ by CH⁺, CH₂⁺, CH₄⁺, N⁺, NH⁺, NH₂⁺, NH₃⁺, O⁺, OH⁺, H₂O⁺, CO⁺, N₂⁺, C₂⁺, and C₂H⁺ ions. Although in most cases hydrogen atom abstraction is the only available exothermic pathway for these reactions at thermal energies, the rate constants measured show that except for O⁺, CO⁺, and N₂⁺, a large fraction of collisions between these ions and H₂ are not reactive. The rate constants measured range from a low of (3±1) × 10⁻¹³ cm³/sec for the NH₃⁺−H₂ reaction to (1.73±0.04) × 10⁻⁹ cm³/sec for the N₂⁺−H₂ reaction. These values compare to the Langevin value of about 1.5 × 10⁻⁹ cm³/sec for collisions between these ions and H₂. An examination was also made for possible thermoneutral hydrogen atom exchange reactions for those ions which do not react with H₂ (CH₅⁺, CH₃⁺, NH₄⁺, H₃O⁺, H₂S⁺, H₃S⁺). The only exchange reaction observed was for collisions between CD₃⁺ ions and H₂, for which a rate constant of (5.1±0.5) × 10⁻¹⁰ cm³/sec was measured.