Electroionization study of acetylene and fragment ions

Abstract

A monoenergetic electron beam, produced by two 127° electrostatic selectors in series, was used to obtain electroionization efficiency curves of acetylene from threshold to 10 eV above threshold. Very high sensitivity measurements of high signal-to-noise ratio of the ionization and appearance energies of C 2H 2 +, C 2H +, C 2 +, CH 2 +, CH +, C + and C 2H 2+ are reported. Hot bands are detected below the C 2H 2 + threshold and features due primarily to autoionizing Rydberg series converging to vibrational excited states of this ion are observed immediately above threshold. A value of 11.92±0.09 eV is deduced for the ionization potential of C 2. The CH 2 ++C − ion pair formation is observed for the first time. All curves have broad structures above threshold except for C 2H 2+. Relatively narrow structures are observed between 12 and 16 eV in the C 2H 2 + data which are caused by negative ion and/or autoionization states.