Electron scattering from chiral molecules

Abstract

Detailed information is given on an experiment which was carried out to investigate the spin-dependent attenuation of electron beams transmitted through a vapour of chiral molecules. The experiment is considered to be the first verification of electron dichroism. A transmission asymmetry for longitudinally polarized electron beams of opposite helicity was observed for , a camphor-like molecule containing an ytterbium atom, and also recently for bromocamphor. Asymmetries of about , which is clearly above the detection limit, were measured for both targets at electron energies between 0.5 and 10 eV. No asymmetry was found when enantiomeric camphor vapour was used as the target, thus contradicting a result which has been previously published by another group. The asymmetry measurements are compared with electron transmission spectra, which show that the energies where resonant temporary-ion formation takes place and those of the extrema of the asymmetry agree to a great extent.

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

“…Such dependence has the mechanical analog of the ability of, e.g., left-handed nuts to be threaded onto left-handed but not right-handed bolts. Chiral asymmetries were first observed in gas-phase electron-molecule collisions by the Münster group in 1995 for quasielastic scattering [3][4][5] (but, see also Refs. [6,7]).…”

“…These mechanisms apply also to the quasielastic transmission of spin-polarized electrons through chiral molecules [16]. Chiral sensitivity of total cross sections has been observed with gas-phase targets only if Z ≥ 35 [3][4][5]. This argues circumstantially for the importance of either a Mott scattering or helicitydensity mechanism but against spin-other-orbit coupling.…”

Electron Dichroism: Interaction of Spin-polarised Electrons with Chiral Molecules

“…This called for further experiments, which were started a few years ago by T. Gay's group (Trantham et al 1995) in the United States and by my group. First we repeated the camphor experiments with considerably increased sensitivity and accuracy.…”

“…This has been a matter of long-standing discussion and speculation. A plausible mechanism was suggested by Ulbricht and Vester (1962) Many experiments have been performed to find a more solid basis for this vague hypothesis. Racemic mixtures, which contain equal numbers of L-and D-enantiomers, were irradiated with polarised electrons in order to find out whether the degradation depends on the handedness of the molecule.…”

“…Before presenting the results, we refer to Fig. 6 which illustrates the experiment from the PhD thesis of Stefan Mayer (Mayer et al 1996). An electron beam of 40% longitudinal polarisation from a GaAs source passes through a gas cell containing the chiral molecules of one handedness, where it is attenuated by a factor of 10 or so.…”