Delayed optical radiation following beam foil excitation of Rydberg states in hydrogenic oxygen ions has been observed in the time range from 1.5 ns to 63 ns. The intensity of the n = 9 → 8 and n = 8 → 7 optical transitions (n is the principle quantum number) is found to be ten times smaller than for the delayed X-ray radiation (n = 2 → 1) measured in previous work. The results rule out initial populations of levels with only angular momentum l = n - 1 as well as populations of levels with only l = 0.