Branching ratios for the fragmentation pathways leading to C₂H₂⁺ in electron–ethylene collisions

The production of C₂H${}_3^{+}$ and C₂H${}_2^{+}$  in the fragmentation of ethylene (C₂H₄) by electron impact, in the 25–800 eV energy range, is investigated using the DETOF technique. The kinetic energy distributions of both species are obtained and the disentanglement of the two different fragmentation pathways leading to the production of C₂H${}_2^{+}$, namely (1) C₂H${}_4^{+}\to$ C₂H₂ ⁺ + H₂ and (2) C₂H${}_4^{+}\to$ C₂H₂ ⁺ + 2H, was performed, providing the absolute cross sections for each channel. It is shown that the branching ratios are independent of the projectile velocity for impact energies above 100 eV, amounting to 80% for channel (1) and 20% for channel (2). (paper)