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_I I 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 various models, as well as the F + H-2 -> HF + H benchmark reaction. Several detailed examples are given in the text.