Photoion spectra in coincidence with threshold electrons near the Kr 3d ionisation limits

Abstract

Photoion spectra of Kr near the 3d ionisation limits have been measured using a threshold electron-photoion coincidence technique. The spectra of Kr2+ and Kr3+ ions show structures corresponding to the 3d-1np Rydberg states below the ionisation limits and to 3d5/2 and 3d3/2 ionisation above the ionisation limits. It is proposed that the lower Rydberg states can decay by emitting threshold electrons through two-step autoionisation, such as Kr 3d-15p to Kr+ 4p-2(1S)6p to Kr2+ 4p-2(3P) and Kr 3d-15p to Kr2+ 4s-14p-2np (n>or=5) to Kr3+ 4p-3. The structures due to 3d threshold ionisation show the effect of post-collision interaction, namely peak shifts and asymmetric profiles. The shifts are almost the same in the Kr2+ and Kr3+ spectra.