Pade 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 procedur e first applies a preconditioning function to the scattering matrix element ; then the remaining residual function is interpolated using Fade approxima tions. The method is illustrated by extracting the leading Regge pole posit ion and residue for the state selected reactions Cl + HCl(upsilon = 1, j = 5) --> ClH(upsilon' = 1, j' = 5) + Cl and I + HI(upsilon = 0, j = 0) --> IH (upsilon' = 0, j' = 2) + I, where upsilon and j are vibrational and rotatio nal quantum numbers respectively. (C) 2000 Elsevier Science B.V. All rights reserved.