Electron optic dichroism in camphor

The transmission of longitudinally polarised electrons through a vapour of optically active isomers was investigated. The transmitted intensities, I(P) and I(-P), measured for the same isomer with electrons of opposite helicity, define a transmission asymmetry A=(I(P)-I(-P))/(I(P)+I(-P)). The experiments were performed at 5 eV electron energy with D(+) and L(-) camphor. The measurements confirm the theoretical predictions based on general symmetry arguments: (i) an asymmetry exists; (ii) the asymmetries observed with targets to opposite handedness are of the same magnitude but of different sign. With an electron polarisation P=-0.28, A(D+)=(23+or-11)*10-4 A(L-)=(-50+or-17)*10-4. The problem of relating these results to theoretical estimates of helicity dependence in scattering from chiral molecules is discussed.