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A search for electron circular dichroism in camphor
Abstract
It is possible in principle to observe electron optical activity, the preferential scattering of longitudinally spin-polarized electrons by a chiral target, or electron optical activity, the rotation of an electron beam's transverse spin polarization about its momentum as it is transmitted through a chiral target. This dissertation is a study concerning electron circular dichroism (ECD) using a camphor target. The first search for ECD was performed by Campbell and Farago (D. M. Campbell and P. S. Farago, J. Phys. B, At. Mol. Opt. Phys. 20, 5133). They looked for the preferential transmission of longitudinally polarized electrons and measured an asymmetry $\rm{\cal A}\equiv(I\sb{\uparrow}-I\sb{\downarrow})/(I\sb{\uparrow}+I\sb{\downarrow}),\ where\ I\sb{\downarrow(\uparrow)}$ is the transmitted intensity of electrons with spins (anti-) parallel to their momentum. Using a camphor target, they found an average effect of ${\cal A}$ = (36 $\pm$ 10) $\times$ 10$\sp{-4}$ at an energy of 5eV. However, this result is 10 to 100 times larger than any expected based on "conventional" theories. This discrepancy served as our impetus to repeat Campbell and Farago's experiment. In this dissertation, a scattering theory based on symmetry of the electron-molecule scattering system will be presented. It is shown that the "parity-violating" effects of ECD and optical activity are allowed. Then, three dynamical theories are outlined, estimating the size of ${\cal A}$ to be expected in an experiment similar to that of Campbell and Farago. The apparatus used to investigate ECD will be discussed as well as the systematic checks performed. In addition to measuring ${\cal A}$ at 5eV, we have verified the existence of a negative ion resonance in camphor (1eV) and its effect on ${\cal A}.$ Our results of this investigation and the methods of data acquisition and analysis will be presented.
Subject Area
Atoms & subatomic particles|Molecules
Recommended Citation
Trantham, Kenneth Wayne, "A search for electron circular dichroism in camphor" (1996). ETD collection for University of Nebraska-Lincoln. AAI9620346.
https://digitalcommons.unl.edu/dissertations/AAI9620346