A flowing-afterglow technique is described for measuring the absolute yield of a radiative product state from ion-electron recombination. The technique is applied to CO2+-e(-) dissociative recombination. The measured yield of CO(a (3)Pi) + O(P-3) is 0.29+/-0.10. This includes cascade from higher triplet states of CO. The vibrational distribution in CO(a (3)Pi,upsilon=0-3) is approximately Boltzmann, with an effective temperature of 4200+/-300 K. The measured rate constant for quenching of CO(a) by CO2 is (1.0+/-0.2) X 10(-11) cm(3) s(-1), somewhat lower than previous measurements.