Functional representation of Liu and Siegbahn's accurate ab initio potential energy calculations for H+H₂

Liu and Siegbahn's recent calculations on the potential energy surface for H+H₂ provide us with the most accurately known potential energy surface for any chemical reaction. We have made an accurate least-squares fit to this surface which satisfies several criteria for use in scattering calculations, including essentially exact agreement with all saddle point properties and being reasonably compact. With eight nonlinear parameters and 15 linear parameters we fit all 267 ab initio points with a root-mean-square error of 0.17 kcal/mol and a maximum absolute deviation of 0.55 kcal/mol. The spherical average of the interaction potential is in good agreement with the recent experimental estimate of Gengenbach, Hahn, and Toennies.