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Numerical Regge pole analysis of resonance structures in elastic, inelastic and reactive state-to-state integral cross sections

We present a detailed description of a FORTRAN code for evaluation of the resonance contribution a Regge trajectory makes to the integral state-to-state cross section (ICS) within a specified range of energies. The contribution is evaluated with the help of the Mulholland formula [Macek et al (2004)] and its variants [Sokolovski et al (2007); Sokolovski and Akhmatskaya (2011)]. Regge pole positions and residues are obtained by analytically continuing S-matrix element, evaluated numerically for the physical values of the total angular momentum, into the complex angular momentum plane using the PADE II program [Sokolovski et al (2011)]. The code decomposes an elastic, inelastic, or reactive ICS into a structured, resonance, and a smooth, "direct", components, and attributes observed resonance structure to resonance Regge trajectories. The package has been successfully tested on several models, as well as the F + H2->HF+H benchmark reaction. Several detailed examples are given in the text.