Spin-dependent electron-molecule scattering

Polarized electrons can experience a variety of spin-dependent effects when they scatter from gaseous molecular targets. If the molecules are chiral, or “handed,” the electrons can experience phenomena that are closely analogous to the well-known optical responses of chiral molecules. This dissertation is primarily concerned with one of these effects: electron circular dichroism (ECD).; A longitudinally polarized electron beam will be attenuated by chiral molecules according to its forward or backward spin direction. Therefore, an asymmetry in the transmitted current can be measured if the electron polarization is modulated. This asymmetry is defined as A = ( I_↑ − I_↓)/( I_↑ + I_↓), where I_↑(↓) is the transmitted intensity of electrons with spins parallel (antiparallel) with their momenta. The first evidence for nonzero transmission asymmetries was seen by Kessler's group in Münster (S. Mayer and J. Kessler, Phys. Rev. Lett. 74, 4803 (1995)) when they investigated ECD in bromocamphor and discovered a maximum asymmetry of 1.7 × 10−4. This dissertation describes our attempts to reproduce this result using new optical techniques, and it sets the stage for future experiments with chiral molecules.; We are also interested in scattering polarized electrons from simple achiral, or non-handed, molecules. We have measured the circular polarization of light emitted from both atomic H and molecular H₂ after bombarding H₂ with longitudinally polarized electrons. For both atomic and molecular fluorescence near threshold we observe a circular polarization as great as 10% of the electron polarization. This represents the first direct observation of spin transfer in electron-molecule collisions.