The generation of the green line of atomic oxygen by dissociative recombination of O-2(+) occurs by the capture of an electron into a repulsive state of O-2 followed by dissociation along another state of a different electronic symmetry. The two states are coupled together by mixed symmetry Rydberg states, Quantum chemical calculations give a rate coefficient at room temperature of (0.39(-0.19)(+0.31)) x 10(-8) cubic centimeters per second. The quantum yield of excited oxygen is within the range deduced from ground, rocket, and satellite observations. The rate coefficients and yields are needed in models of the optical emission, chemistry, and energy balance of planetary ionospheres.