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Failure to observe electron circular dichroism in camphor

1995; IOP Publishing; Volume: 28; Issue: 17 Linguagem: Inglês

10.1088/0953-4075/28/17/004

1361-6455

Kenneth Trantham, Mark Johnston, T. J. Gay,

Advanced Physical and Chemical Molecular Interactions

We have searched for evidence of electron circular dichroism, Lhe Preferential transmission of longirudinally polarized electrons lhrough a chiral medium, using stereoisomers of camphor. Such an effect was seen by Campbell and Farago in 1987 for 5 eV elecvons. Within OUT detection limit (- 0.02%) we have not observed asymmehic transmission at either an incident electron energy of 1 eV or 5 eV. ln preption for this inquiry, we also measured the total sanering cross section for camphor in the energy range 0.5-5 eV. Optical activity is the rotation of the plane of polarization of linearly polarized light as it passes through a chiral medium. A complementary phenomenon is circular dichroism: the preferential absorption of left- or right-handed circularly polarized light in a chiral medium. Farago (1980, 1981) pointed out that symmetry allows similar phenomena to be observed with electrons. Thus 'electron optical activity' is the rotation of a transverse electron spin vector in a plane perpendicular to the momentum in a chiral medium. Similarly, 'electron circular dichroism' is the preferential absorption of left- or right-handed longitudinally- polarized electrons in a vapour of chiral molecules. These parity violating effects arise because the target molecule lacks inversion symmetry. Electron circular dichroism also causes scattered electrons that were initially unpolarized to develop a polarization component in the plane of scattering. Beerlage ef al (1981) first searched for this effect but failed to see it within their experimental limits. A different experiment, performed by Campbell and Farago (1987). looked for preferential transmission of longitudinally polarized electrons through stereoisomers of camphor. They measured the mymetry