Inclusion of nonadiabiatic effects in calculations on vibrational excitation of molecular hydrogen by low-energy electron impact

The nonadiabatic phase matrix method offers a unified, systematic treatment of vibrational dynamics in calculations of low-energy inelastic electron-m olecule cross sections. This formalism uses fu;ed-nuclei R matrices to desc ribe the region of configuration space near the target but-unlike its fully adiabatic counterpart, the energy-modified adiabatic method-includes nonad iabatic effects, which are important for resonant scattering and near a vib rational threshold. A most stringent test of this method is e-H-2 scatterin g below 10 eV, where elastic and inelastic cross sections exhibit an enhanc ement around 3 eV which at the fixed-nuclei level involves a range of physi cal effects, from nonresonant to resonant scattering, as the internuclear s eparation varies from the smallest to largest relevant values. Here we desc ribe an implementation of this method appropriate to such systems, an asses sment of its accuracy for e-H-2 scattering, and an appraisal of the importa nce of nonadiabatacity for the 0-->1 and 0-->2 vibrational excitations. [S1 050-2947(99)08901-5].