The dissociative ionization of C2H2 and C2D2. The [CH(CD)]+ dissociation channel. The H(D)CC(D) H binding energy Original Research Article

The dissociative electroionization of C2H2(C2D2) has been investigated in CH+(CD+) dissociation channel. The translational energy distribution of the fragment ion has been examined as a function of the electron energy between 20 and 99 eV. The first differentiated ionization efficiency curve has been measured for KE(CH+) = 0.0−6.0 eV. Threshold energies of CH+ and CD+ have been measured and the effect of isotopic substitution is discussed. From the lowest onset of both CH+ and CD+, and from the kinetic energy measurements, the CC bond strength has been derived, i.e. D0(HCCH) = 9.83±0.10 eV. Higher appearance energies are assigned and reaction mechanisms are proposed. Above 34 eV electron energy, the CH+ ions carrying 2.0–5.5 eV kinetic energy are produced through Coulomb explosion of C2H22+ states.