DOUBLE AND SINGLE IONIZATION OF NEON, ARGON AND KRYPTON IN THE THRESHOLD REGION STUDIED BY PHOTOELECTRON ION COINCIDENCE SPECTROSCOPY

Photoionization and photo-double ionization of neon, argon and krypton have been studied in the threshold region for double ionization by measuring coincidences between zero energy photoelectrons and the singly or doubly charged product ions (TPEPICO technique). The efficiency of this technique has been much improved by the use of the penetrating field method for the detection of both the photoelectrons and the ions. The observations show that autoionization of satellite states makes a dominant contribution to the double ionization process and that these states decay solely into this channel when it is energetically allowed. Beta parameter measurements up to 2 eV above the double ionization potential of argon for electrons correlated to Ar2+ ions do not reveal the behaviour expected from theoretical predictions.