The peak at ca. 140 K corresponds to desorption of the more weakly bound state.

Rationale

The more weakly bound state has the lower activation energy for desorption and will therefore undergo desorption at a lower temperature.

The two peaks correspond to the presence of both molecularly and atomically (i.e. dissociatively) adsorbed oxygen on the surface.

The molecular species is the more weakly adsorbed.

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