The Dissociative Electroionization of C2H2, C2D2 and C2HD. Investigation of the [C2H(D)]+ and [H(D)]+ Dissociation Channels. The (D)H-C2H(D) binding energy.

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 the 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. The ionization efficiency of the doubly ionized molecular ion is observed for the first time in C2HD isotopic species.