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Asymmetric interactions between spin-polarized electrons and chiral molecules
All molecular forms of life possess a chiral asymmetry, with amino acids and sugars found respectively in L- and D-enantiomers only. The primordial origin of this enantiomeric excess is unknown. One possible explanation for this is given by the Vester-Ulbricht hypothesis [Ulbricht, T.L.V. & Vester, F., Tetrahedron 18, 629-637 (1962)], which suggests that left-handed electrons present in beta-radiation, produced by parity-violating weak decays, interacted with biological precursors of DNA and preferentially destroyed one of the two enantiomers. Experimental tests of this idea have thus far yielded inconclusive results. This dissertation presents research that searches for asymmetric interactions between spin-polarized electrons and chiral molecules. The first experiments discussed consider the transmission of longitudinally spin-polarized electrons through chiral molecules. In 1995, Mayer and Kessler reported an asymmetry in such a process using chiral bromocamphor molecules [S. Mayer and J. Kessler, Phys. Rev. Lett. 744, 803 (1995)]. A confirmation of these results is presented. In addition to transmission experiments though, asymmetric effects were also detected in dissociative electron attachment (DEA). The primary focus of this dissertation was investigating DEA interactions between chiral molecules (AB) and spin-polarized electrons (e-). Such a collision can be represented by AB + e- → A + B-. An asymmetric interaction of the spin-polarized electrons with the chiral bromocamphor molecules was detected by measuring a difference in the negative ion current produced by DEA that was dependent on the spin-polarization of the incident electrons. This experiment provides direct evidence for chirally-dependent bond breaking when spin-polarized electrons are incident upon gas-phase chiral molecules, which offers unambiguous evidence for a well-defined, chirally-sensitive destructive molecular process and, as such, circumstantial evidence for the Vester-Ulbricht hypothesis.
Dreiling, Joan Marie, "Asymmetric interactions between spin-polarized electrons and chiral molecules" (2014). ETD collection for University of Nebraska - Lincoln. AAI3618568.