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) a s well as the formation of PEs by delayed pulsed-field ionization (PFI -PE) has been investigated in photoelectron photoion coincidence (PEPI CO) experiments employing synchrotron radiation. Direct ZEKE-PEs and d elayed PFI-PEs can easily be distinguished by their time of flight if a small static background field is applied. Coincidence experiments ha ve 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 f ree from the influence of delayed pulsed-field ionization. To our know ledge this is the first report of a pure PFI photoelectron spectrum (P FI-PES) recorded with synchrotron radiation.