The distinction of direct and pulsed-field ionized zero kinetic energy photoelectrons in electron/ion coincidence experiments

The direct formation of zero kinetic energy photoelectrons (ZEKE-PE) as well as the formation of PEs by delayed pulsed-field ionization (PFI-PE) has been investigated in photoelectron photoion coincidence (PEPICO) experiments employing synchrotron radiation. Direct ZEKE-PEs and delayed PFI-PEs can easily be distinguished by their time of flight if a small static background field is applied. Coincidence experiments have been performed between either one direct ZEKE-PE or one PFI-PE and the corresponding photoion in the photoionization of argon atoms. The experiments prove that previous ZEKE-PEPICO experiments of our group [Chem. Phys. Letters 224 (1994) 371; Chem. Phys. 187 (1994) 117] were free from the influence of delayed pulsed-field ionization. To our knowledge this is the first report of a pure PFI photoelectron spectrum (PFI-PES) recorded with synchrotron radiation.