EXACT QUANTUM MONTE-CARLO CALCULATIONS OF THE POTENTIAL-ENERGY SURFACE FOR THE REACTION H-2-]+H-2+H(H)

We report ''exact'' quantum Monte Carlo calculations of the potential energy surface for the reaction H+H-2->H-2+H. The method used is free of systematic error. The statistical or sampling error was reduced to +/- 0.10 kcal/mol for several hundred points distributed across the su rface, to +/- 0.02 kcal/mol for the minimum energy approach of H to H- 2, to +/- 0.02 kcal/mol near the saddle point, and to +/- 0.01 kcal/mo l at the saddle point. The upper and lower surfaces in the region of t he Jahn-Teller cusp were determined with a statistical error of +/- 0. 2 kcal/mol.