At high surface temperatures, CO and O desorb, thus lowering the surface oxygen coverage, but as the coverage reduces, the barrier to form CO increases . Once the energy barriers are greater than the available thermal energy, the desorption process shuts down and the surface reaches a quasi-steady transient coverage that depends on the supply of O atoms from the incident beam. In the experiments with the pulsed hyperthermal O/O2 beam, when a subsequent beam pulse arrives at the sample, a new dose of O atoms on the surface lowers the energy barriers, resulting in further CO desorption until a new quasi-steady transient state is achieved. This is a continual process where the incoming beam pulse aids in removing a subset of functional groups, and this continuous process occurs until the surface reaches a steady state over the course of minutes to hours. As has been discussed previously , a high flux of O atoms, especially from a continuous rather than a pulsed source, reduces hysteresis. Thus, the maintenance of a high surface coverage at all times would be expected to result in the same temperature-dependent reactivity regardless of whether the temperature is increasing or decreasing.