The passage of a beam of transversely polarised electrons through a sample of chiral (oriented and non-oriented) molecules is considered. The behaviour of the electronic spins, in particular the rotation of the initial polarisation vector, is discussed for various cases: (i) passage through an optically active refractive medium, (ii) forward scattering from oriented molecules and (iii) scattering from chiral randomly oriented molecules. Numerical results are presented for forward scattering from a chiral model molecule and the influence of the molecular orientation relative to the direction of the initial polarisation vector is discussed.

The attenuation of a longitudinally polarized electron beam in an optically active medium is discussed. A general theory is developed and numerical results are presented for a chiral model molecule.

The R-matrix method is extended to treat electron scattering from molecules containing a heavy atom. It is then used to calculate low energy total elastic and vibrational excitation cross sections for e--HBr scattering. Results are obtained at the equilibrium internuclear separation using two approximations: the first in which polarization effects are represented by the inclusion of quadratically integrable correlation functions and the second in which polarized pseudostates as well as the target ground state are retained in the total wavefunction expansion. The calculations using the first approximation are carried out for a range of internuclear separations and the vibrational motion is then included using a non-adiabatic R-method approach. A low energy 2 Sigma resonance is found in the fixed-nuclei calculations which gives rise to sharp threshold peaks in the vibrational excitation cross sections in qualitative accord with experiment. These peaks are interpreted as being due to the nuclear excited Feshbach resonance mechanism.

Earlier ab initio calculations for electron scattering by HBr are analysed to obtain the behaviour of the S-matrix poles in the complex momentum plane as a function of the internuclear distance. This analysis shows the existence of a pole corresponding to a bound state at large internuclear distances as well as a pole corresponding to a shape resonance at small internuclear distances. It is found that the bound-state pole does not evolve into the shape resonance pole as the internuclear distance decreases but instead splits into two mirror image poles which move onto unphysical Riemann sheets of the complex momentum plane confirming model-potential calculations by Herzenberg and Saha. The physical implications of the mirror image poles and the shape resonance pole are also discussed.