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

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 7.6x10(-13) cm(2) for C2H+ and 1.7x10(-12) cm(2) 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+.