LOW-ENERGY-ELECTRON SCATTERING BY HBR

The R-matrix method is extended to treat electron scattering from mole cules 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 separ ation using two approximations: the first in which polarization effect s are represented by the inclusion of quadratically integrable correla tion functions and the second in which polarized pseudostates as well as the target ground state are retained in the total wavefunction expa nsion. 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 give s rise to sharp threshold peaks in the vibrational excitation cross se ctions in qualitative accord with experiment. These peaks are interpre ted as being due to the nuclear excited Feshbach resonance mechanism.