The appearance energy of C2H+ from C2H2 revisited. A photoion-photoelectron coincidence spectroscopic determination

✍ Scribed by Ch. Servais; R. Locht

• Publisher: Elsevier Science
• Year: 1995
• Tongue: English
• Weight: 705 KB
• Volume: 236
• Category: Article
• ISSN: 0009-2614
• DOI: 10.1016/0009-2614(95)00182-4

✦ Synopsis

The dissociative ionization of C2H 2 in a C2H+-producing channel has been reconsidered. The photoion-photoelectron coincidence (PIPECO) technique has been used The C2H+/e -coincidence rate curve has been recorded between 16.2 and 21.2 eV. The lowest appearance energy determined for C2 H+ is 17.35 ± 0.04 eV. A second appearance energy is measured at 18.40 ± 0.04 ¢V. At both energies ethyny! ions are produced through a predissociation mechanism at the expense of the C2H 2 (A~Ag) state at 17.35 eV and C2H~'(B 2:~ ) at 18.40 eV. These results are in good agreement with the most recent TPIPECO experiments and dissociative electroionization results. This comparison leads to the exclusion of any contribution of autoionization phenomena to the C 2 H + ion production between 16.2 and 21.2 eV. Investigations of C 2 H + through the ion pair formation channel (and the dissociative electron attaci~ment producing C2H-and H-) in C2H 2 are reported and its contribution to C2 H+ ion production below 17.3 eV must be d~scarded.