A model calculation of the potential-energy function of two H atoms around a Pt atom that protrudes from a smooth metallic-Pt surface has been performed using the Heitler-London method. It is found that the potential energy is minimum along two contours; along one contour, the two H atoms combine as a molecule, while along the second contour, they are separated not only geometrically but also electronically when the Pt-H separation is larger than about 2.4a₀.