MODIFIED EFFECTIVE RANGE THEORY AS AN ALTERNATIVE TO LOW-ENERGY CLOSE-COUPLING CALCULATIONS

We investigate the feasibility of using modified effective range theory to 'project' results of theoretical scattering calculations to energies so low that such calculations are numerically intractable. In particular, this theory as developed by Fabrikant in the body-frame fixed-nuclei formulation of electron scattering from non-polar molecules provides expansions of the reactance matrix that enable determination of the scattering length (and other parameters as needed) and total cross sections with greater accuracy and over a larger range of energies than do conventional implementations of such expansions for the total cross section. We have explored the viability, accuracy and potential problems of this stratagem for the e-H-2 and e-N2 systems; in both cases, careful use of these expansions enables calculation of highly accurate cross sections at very low energies without recourse to numerically problematic, CPU-intensive close-coupling calculations.