A potential-energy (reaction) surface for a process A + B–C in which the initial descent of the system into the product valley is associated with a substantial decrease in the A–B distance and with little separation between the products A–B and C. In terms of a potential-energy profile, the energy barrier occurs in the early stage of the reaction path. Attractive surfaces are also called early-downhill surfaces, and the barrier in such a surface is called a Type-I barrier.