Large curvature ground state

The site dependence of the PES is more than just a variation of the barrier energy and distance from the surface, the early/lateness of the barrier and the curvature of the elbow PES can also change. This leads to a spatial separation of different processes, as noted above, for H2 on Cu surfaces, dissociation of the vibrational ground-state molecules is dominated by the bridge sites, while molecules vibrationally excite/de-excite largely at the atop site. In fact, site specificity of reactivity is also state specific [45]. Thus for H2/Cu(1 0 0), the bridge site is the most favoured for dissociation of vibrationally cold molecules, but the atop site is the most favoured for vibrationally excited molecules, as shown in Fig. 4. 

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