Resonance effects in low energy electron scattering by HCl

Earlier ab initio calculations for electron scattering by HCl are analysed to obtain the behaviour of the S-matrix poles as the internuclear distance is varied. It is shown that the pole which corresponds to a bound state at large internuclear distances does not evolve into a resonance as the distance is decreased but moves on to a lower Riemann sheet where it will have no observable effect on scattering cross sections. The resonance which was observed near 3 eV is shown to correspond to a different, unrelated pole.