The dissociative electroionization of C2H2, C2D2 and C2HD: Investigation of the [C2H(D)]+ and [H(D)]+ dissociation channels.The (D)H-C2:H(D) binding energy Original Research Article

The dissociative electroionization of C2H2 in the H+ and C2H+ dissociation channels has been extensively investigated in C2H2 and C2D2. The kinetic energy distributions and ionization efficiency curves of both species were examined in detail. The H+(D+) ion shows its lowest onset energy at 18.93 ± 0.2 eV, whereas the C2H+ is produced at 17.30 ± 0.11 eV. For the H+-producing channel, the kinetic energy (KE) versus appearance energy (AE) diagram is obtained, extensively discussed and the bond dissociation energy D(H-C2H) = 5.33 ± 0.23 eV is estimated. This value is compared and discussed with respect to the values found in the literature. Predissociation and dissociative autoionization are the dominant H+-producing mechanisms. At high electron energies doubly ionized states of C2H2 are involved. For C2H+ beside the threshold at 17.30 ± 0.11 eV a new onset at 18.27 ± 0.10 eV is observed. These thresholds are discussed. The formation of the doubly ionized species C2H2+, observed in the mass spectrum of C2H2, is investigated. The ionization efficiency of the doubly ionized molecular ion is observed for the first time in C2HD isotopic species.