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

Abstract

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 3×10^{-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.

Anomalously Large Chiral Sensitivity in the Dissociative Electron Attachment of 10-Iodocamphor

“…Electron-spin-dependent asymmetries were determined using a lock-in amplifier to detect the change in target-cell-wall current at the frequency of the electron helicity reversal. Checks of our measurements [11,25] confirmed our ability to measure chirally dependent asymmetries less than 10 −4 , validated our detection of a negative ion current from DEA, and provided an upper limit of ≤ 20% (and, more typically, < 8%) for scattered-electron contributions to the DEA signal.…”

“…In our work, we used bromocamphor (C 10 H 15 BrO) and monitored the production of Br anions [11]. The observation of chiral sensitivity in a breakup reaction is important because, among other things, it validates the premise of the Vester-Ulbricht hypothesis regarding the origins of biological homochirality [12].…”

“…Figure 3 shows the DEA asymmetry for the molecules we investigated through a range of electron energies near 0 eV. To explore the effect of Z on A, we compared our previously-measured asymmetries for 3-bromocamphor (referred to below as 3Br for brevity) [11] with those of 3-iodocamphor (3I). Additionally, we studied the effect of constitution on the chiral asymmetry by investigating the constitutional isomer 10-iodocamphor (10I).…”

“…To this end, we varied Z 2 from 1225 (Br) to 2809 (I) and changed the position of the heavy atom within the molecule to probe the role of its proximity to a chiral center. Our apparatus [11] has four main components: an active-feedback optical system, a polarized electron source, a target chamber, and an optical electron polarimeter. The source of longitudinally spin-polarized electrons is a GaAs photocathode [23].…”

Projectile Spin and Stopping Power

“…Recently there has been reported a small effect of the chirality of some molecules for measuring molecular dissociative electron attachment (DEA) as a function of low energy electron beam helicity [6]. In particular, beams of spin pure electrons gave different breakup patterns for chirally different targets, for example the enantiomers differently spin states of the projectile proton.…”