Padé reconstruction of Regge poles from scattering matrix data for chemical reactions

We describe a practical procedure for analytically continuing a scattering matrix element into the complex angular momentum plane, given its values at the physical angular momentum quantum numbers of 0, 1, 2, …. The procedure first applies a preconditioning function to the scattering matrix element; then the remaining residual function is interpolated using Padé approximations. The method is illustrated by extracting the leading Regge pole position and residue for the state selected reactions Cl+HCl(v=1, j=5) → ClH(v′=1, j′=5)+Cl and I+HI(v=0, j=0) → IH(v′=0, j′=2)+I, where v and j are vibrational and rotational quantum numbers respectively.