Complex Kohn variational method: Application to low-energy electron-molecule collisions

An algebraic variational method, based on application of the Kohn principle to the T matrix, is formulated for multichannel scattering problems and applied to the case of low-energy electron-molecule collisions. The method requires only Hamiltonian matrix elements and is anomaly-free. The present formulation is noteworthy in that it requires no bound-free nor free-free exchange matrix elements. The new technique is illustrated by application to $e^{\mathrm{-}}$+${\mathrm{H}}_2$ scattering in both the static-exchange and the two-state approximations. The method is found to be both efficient and accurate.