Chirally Sensitive Electron-Induced Molecular Breakup and the Vester-Ulbricht Hypothesis

We have studied dissociative electron attachment in sub-eV collisions between longitudinally polarized electrons and chiral bromocamphor molecules. For a given target enantiomer, the dissociative Br anion production depends on the helicity of the incident electrons, with an asymmetry that depends on the electron energy and is of order $3\times {10}^{-4}$. The existence of chiral sensitivity in a well-defined molecular breakup reaction demonstrates the viability of the Vester-Ulbrict hypothesis, namely, that the longitudinal polarization of cosmic beta radiation was responsible for the origins of biological homochirality.

Figure 1

Polarized electron source and target chamber. (1) Laser beam from active-feedback system for the GaAs source, (2) solenoidal guiding magnets, (3) GaAs photocathode, (4) NEA activation cesiators, (5) gate valve, (6) chiral target cell (see also Fig. 2), (7) optical polarimeter target cell, (8) fluorescence collection lens, (9) window for the optical polarimeter. The bend in the apparatus eliminates the line of sight between the target cell and the GaAs crystal to minimize chemical contamination of the NEA photocathode.

Figure 2

Detail of the target vapor cell, showing the incident ($I_0$) and transmitted ($I_{\mathrm{F}\mathrm{C}}$) electron beams, the target cell structure, lens elements 1–10, and the Faraday cup assembly used to measure the transmitted beam.

Figure 3

Top: DEA current, with the range of energies where asymmetry data were taken indicated by the dotted vertical lines. Bottom: The asymmetry in DEA current as a function of target cell retarding voltage. Squares and circles represent opposite settings of the quarter-wave plate that circularly polarizes the laser light, which should give asymmetry measurements of opposite signs. A positive sign for the data represented as squares corresponds to a positive sign for the data of Nolting et al. [25] with ($-$) bromocamphor. The triangles indicate data taken with racemic bromocamphor. Uncertainties are determined by taking the standard deviation of the mean of the individual asymmetry measurements.

Figure 4

The fraction of the attenuated current that is detected on the inner target cell walls.

Figure 5

Component of the inner target cell current due to scattered electrons, $\alpha$, as a function of target retarding voltage for different assumptions about $C_{\mathrm{DEA}}$. The curves represent quadratic fits to the data, which are distributed about their respective fits with a standard deviation of $\sim 0.03$.