I. Electron-impact ionization and dissociation of C2H2+ and C2D2+

Absolute cross-sections for electron-impact ionization and dissociation of C2H2+ and C2D2+ have been measured for electron energies ranging from the corresponding thresholds up to 2.5 keV. The animated crossed beams experiment has been used. Light as well as heavy fragment ions that are produced from the ionization and the dissociation of the target have been detected for the first time. The maximum of the cross-section for single ionization is found to be (5.56 ± 0.03)*10-17 cm2 around 140 eV. Cross-sections for dissociation of C2H2+ (C2D2+) to ionic products are seen to decrease for two orders of magnitude, from C2D+ (12.6 ± 0.3)*10-17 cm2 over CH+ (9.55 ± 0.06)*10-17 cm2, C+ (6.66 ± 0.05)*10-17 cm2, C2+ (5.36 ± 0.27)*10-17 cm2, H+ (4.73 ± 0.29)*10-17 cm2 and CH2+ (4.56 ± 0.27)*10-18 cm2 to H2+ (5.68 ± 0.49)*10-19 cm2. Absolute cross-sections and threshold energies have been compared with the scarce data available in the literature. (authors)