The ab initio potential energy surfaces pertinent to Zn(P-3) + H-2 --> ZnH((2) Sigma) + H have been calculated and are described. For thermal collisions, the dominant reactive surfaces is identified and a mechanism for the reaction on this surface, which may explain the rotational state populations in the ZnH products, is proposed. A novel dynamical technique of running classical simulations on nb initio surfaces, using a piecewise tessellation rather than a global functional fit, is briefly introduced with sample trajectories shown.