Direct calculation of complex resonance poles in electron-molecule scattering using separable T-matrix expansions

The complex resonance poles of the S matrix for electron-atom or electron-molecule scattering are calculated directly using separable expansions of the potential (and thus of the T matrix) within the framework of the many body optical potential approach. The performance of the method is demonstrated for the well known 2.3 eV shape resonance in electron-N₂ scattering. The authors present the first direct calculation of this resonance pole at the equilibrium geometry of N₂ including both polarisation and target correlation.