In the O-P process, as the neutron fuses to the target nucleus, the deuteron binding force pulls the "proton end" closer than a naked proton could otherwise have approached on its own, increasing the potential energy of the positive charge. As a neutron is captured, a proton is stripped from the complex and is ejected. The proton at this point is able to carry away more than the incident kinetic energy of the deuteron since it has approached the target nucleus more closely than what is possible for an isolated proton with the same incident energy. In such instances, the transmuted nucleus is left in an energy state as if it had fused with a neutron of negative kinetic energy. There is an upper bound of how much energy the proton can be ejected with, set by the ground state of the daughter nucleus.