EFFICIENCY OF HIGH-N RYDBERG-STATE STABILIZATION IN PULSED-FIELD IONIZATION ZERO-KINETIC-ENERGY PHOTOELECTRON-SPECTROSCOPY

To examine the issues concerning Rydberg-state stabilization in pulsed -field ionization zero-kinetic-energy (PFI-ZEKE) photoelectron spectro scopy, spectra at the first and second ionization thresholds of argon have been taken under different ion-density conditions. These provide a contrast between the signals from autoionizing and nonautoionizing R ydberg series. A careful comparison between the PFI-ZEKE spectra and r elative partial photoionization cross sections provides the first meas urement of the efficiency of stabilization in PFI-ZEKE spectroscopy. T his efficiency or quantum yield varies at the second ionization thresh old with changing ion density and principal quantum number, introducin g ion-density-dependent line-shape distortions. These changes may be a scribed to the competition between stabilization and autoionization of the Rydberg states and its variation with principal quantum number.