Near-threshold rotational excitation in electron-polar-molecule scattering

Variational R-matrix calculations have been performed for electron scattering by the HF molecule. Calculations over a grid of internuclear distances are used to compute the vibronic R-matrix, using a new adiabatic phase matrix method described here. This body-frame vibronic R-matrix is converted to the rovibronic R-matrix by a modified frame transformation at the R-matrix boundary. The external rovibronic close-coupling equations are solved by analytic methods. This methodology makes it feasible to carry out full first-principles calculations including molecular rotation and vibration, although only vibrationally elastic results are reported in the present paper. The threshold behaviour of the body-frame results can be described in terms of dipole eigenfunctions. Validity in the laboratory frame show that influence of rotation on vibrationally elastic e-HF collisions. The computed cross sections at small energies, close to the rotational thresholds, show rather sharp peaks that are dominated by j to j+or-1 excitations.