Improved accuracy in adiabatic cross sections for low-energy rotational and vibrational excitation of molecules by electron impact

We have developed a first-order adiabatic scattering theory for the calculation of low-energy rovibrational cross sections. This theory is more efficient computationally than a full coupled-state method because it transforms coupling of intermediate states into a parametric dependence on nuclear coordinates, and it is more accurate than the conventional adiabatic nuclei method because it correctly conserves energy in the entrance and exit channels. As formulated, this theory can easily be implemented using available computer programs that solve fixed-nuclei scattering equations. We derive this theory for rotational and vibrational excitation with both local and nonlocal potentials and assess it by application to e-H₂ collisions.