Dissociative recombination of C2H+ and C2H4+: Absolute cross sections and product branching ratios

Abstract

Dissociative recombination (DR) of the hydrocarbon ions C₂H⁺ and C₂H₄⁺ has been examined at the heavy-ion storage ring CRYRING (Manne Siegbahn Laboratory, Stockholm, Sweden). Absolute DR cross sections were measured for center-of-mass collision energies between 1 meV and 0.1 eV for both ions, giving cross sections at 1 meV of 7.6 × 10⁻¹³ cm² for C₂H⁺ and 1.7 × 10⁻¹² cm² for C₂H₄⁺. The dissociative recombination branching ratios were determined at minimal collision energy, showing that the carbon bond is broken in 57% of the dissociative recombination events for C₂H⁺, while this happens in only 7% of the events for C₂H₄⁺. In the case of C₂H₄⁺, three-particle breakup into C₂H₂ and 2H is the dominant product channel with a branching ratio of 66%. The present results are compared with previous DR measurements made at CRYRING for DR of C₂H₂⁺ and C₂H₃⁺.