L. Liljeby

Photoion Auger-electron coincidence measurements near threshold

Abstract The vacancy cascade which fills an atomic inner-shell hole is a complex process which can proceed by a variety of paths, often resulting in a broad distribution of photoion charge states. We have measured simplified argon photoion charge distributions by requiring a coincidence with a K-LL or K-LM Auger electron, following K excitation with synchrotron radiation, as a function of photon energy, and report here in detail the argon charge distributions coincident with K-L1L23 Auger electrons. The distributions exhibit a much more pronounced photon-energy dependence than do the more complicated non-coincident spectra. Resonant excitation of the K electron to np levels, shakeoff of these np electrons by subsequent decay processes, double-Auger decay, and recapture of the K photoelectron through postcollision interaction occur with significant probability.

Observation of zero field quantum beats in gas-excited helium projectiles

Zero-field quantum beats in the decay of the 3p3P level in HeI have been observed under approximately single-collision conditions using fast4He+ projectiles excited in a short gas-cell. The frequency, amplitude and phase of the beat signal are compared with theory and results from multiple collision experiments using foil excitation.

Angular distributions of single- and double-electron capture in very-slow Ar6+-Ar collisions

Abstract We have measured state-resolved angular distributions of one- and two- electron capture in 32 to 800 eV Ar 6+ -Ar collisions. The experimental energy-gain spectra show that single-electron capture mainly populates the 5s, 5p and 4f levels. We observe detailed structures in the corresponding angular distributions, but a final interpretation has to await a quantitative analysis of the collision dynamics. We tentatively ascribe the main features in the angular distribution of true double-electron capture at Q 26 eV (4s4f and 4s5s) and Q 42 eV (3d4d) to processes involving two consecutive one-electron transitions. For the transfer ionization process, we measure a Q -value of ∼ 26 eV, which we assign to autoionizing 4s5s (or 4s4f) levels. The 4s5s, 4s4f, and 3d4d levels all reside above the first ionization limit of Ar 4+ but we find that the 3d4d level stabilizes through radiative decay.

Convoy Electrons from Solids in Coincidence with the Final Projectile Charge State

We measure the yield and final velocity distribution of electrons accompanying the projectile exiting from thin solid targets in coincidence with the projectile charge state. We find that the yield per emergent projectile and the longitudinal velocity distribution is independent of the final projectile charge state.