Computational study and complex angular momentum analysis of elastic scattering for complex optical potentials

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Abstract
A systematic study of elastic scattering by complex valued optical potentials has been carried out. A Lennard-Jones (12,6) potential with an imaginary r−s term has been used in the calculations. The collision parameters are chosen to model the elastic scattering of K by HBr and Li by HBr. First-order semiclassical single turning point phase shifts are compared with accurate quantum phase shifts and close agreement is found. It is straightforward to calculate semiclassical phase shifts for an optical potential; it is unnecessary to introduce additional approximations (for numerical convenience) as is usually done in the literature. Up to 15 000 terms in the partial wave series are used to calculate elastic angular distributions. It is shown that a rich interference structure and a backward glory can occur in the large angle scattering, provided the transition from absorbency to transparency is sufficiently rapid. Different optical potentials can result in similar angular distributions. A complex angular momentum (Regge pole) analysis of the large angle scattering has been carried out. It is shown that the interference effects have a physical interpretation in terms of surface waves that propagate around the core of the potential and the directly reflected elastic scattering.