Heavy particle intereference and diffraction in fast electron transfer collisions

by Mr Magnus Gudmundsson (Stockholms Universitet)

Friday 3 Jun 2011, 13:00 → 16:00 Europe/Stockholm

FB42

This thesis presents experimental results from the synchrotron cooler and storage ring CRYRING on charge transfer processes in fast electron transfer collisions using high-resolution cold target recoil-ion momentum spectroscopy. The main focus of these studies was to investigate a key concept of quantum mechanics: the wave-particle duality. One series of experiments has been dedicated to the study of heavy particle de Broglie wave interference due to scattering on a molecular ’double slit’. This is a fundamental manifestation of the wave properties of matter. Quantum interference oscillations were observed in the target orientation dependent cross section of single- and double-electron capture from H2 to 1.3 MeV protons and to 1.2 and 2.0 MeV He2+ ions. Another study, included in this work, is a series of angular differential cross section measurements for single-electron capture to 1.3-12.5 MeV kinetic energy protons from He that enabled us to systematically investigate the classically allowed non-radiative electron capture process in fast collisions predicted by L. H. Thomas in 1927. The cross section for this process is expected to have a nonrelativistic, asymptotic dependence on the projectile velocity, vp, of vp −11. This prediction (from 1927) was verified experimentally for the first time through the present measurements. Using the above mentioned experimental data in addition to measurements of double electron capture by 6.0 MeV He2+ from He, we have also studied the dominating, central part of the angular differential cross section, dσ/dΩ, where the peak shapes and widths surprisingly are very similar regardless of projectile energy and the number of captured electrons. We explain this with a diffraction model for the electron capture and calculate the corresponding diffracting electron capture ‘apertures’ from the shapes and widths of the measured cross sections and the projectile de Broglie wavelengths. We have on one hand established very strong experimental support for the picture suggested by Thomas in 1927 in which electrons and protons are described as classical particles. On the other hand, the diffraction picture describes the shapes of the central peaks in dσ/dΩ quite well, and nicely explains appearances of second and a third maxima in the angular differential cross section. It is hard to see how these seemingly contradicting results can be explained through complementary classical and quantum descriptions of the same underlying physical processes.