RESONANCE EFFECTS IN LOW-ENERGY-ELECTRON SCATTERING BY HBR

Earlier ab initio calculations for electron scattering by HBr are anal ysed to obtain the behaviour of the S-matrix poles in the complex mome ntum plane as a function of the internuclear distance, This analysis s hows the existence of a pole corresponding to a bound state at large i nternuclear distances as well as a pole corresponding to a shape reson ance at small internuclear distances. It is found that the bound-state pole does not evolve into the shape resonance pole as the internuclea r distance decreases but instead splits into two mirror image poles wh ich move onto unphysical Riemann sheets of the complex momentum plane confirming model-potential calculations by Herzenberg and Saha. The ph ysical implications of the mirror image poles and the shape resonance pole are also discussed.