The system O₂/Pd (111) was probed with EELS and thermal desorption spectrometry. The coincidence of 3 peaks in thermal desorption and the O-O region of the EELS spectrum was noted previously and a one-to-one correspondence between the states resolved in EELS and the desorption features was assumed. The authors show that this assumption is incorrect. The lowest binding energy state correlates with the highest frequency vibrational state. The lowest vibrational frequency state acts as a precursor to dissocn. The 2 higher temp. thermal desorption features both arise from the remaining state.