Collisional and electric field effects in the delayed pulsed field ionization zero-kinetic-energy photoelectron spectrum of argon

Abstract

The pulsed field ionization (PFI) zero-kinetic-energy (ZEKE) photoelectron spectrum of argon has been recorded in the region of the transition from the ground neutral state (1S0) to the first two ionization limits corresponding to the two spin–orbit levels (2P3/2 and 2P1/2) of the ground state of the ion. The high-n Rydberg states (85<n<200) belonging to the series converging to the upper spin–orbit state have a lifetime which is more than 50 times longer than expected for the optically accessible ns′ and nd′ series. A series of experiments with pulsed and continuous electric fields of different magnitude shows that the nature and the lifetimes of the high-n Rydberg states probed by ZEKE spectroscopy depend critically on the experimental conditions, in particular on electric field and collisional effects. New experimental results are presented which contribute to a better understanding of the mechanisms which lead to the formation of the unexpectedly long-lived states which are observed in ZEKE spectroscopy.