A broader volcano of α of 0.4 in Fig. limits the overall speed achievable for a given amplitude; the purple points above the curve are further apart and at lower turnover frequencies. This translates to lower overall reaction rates at resonance conditions as shown in Fig. . At the extreme case where the activation energy of the surface reaction does not change with the binding energy of an adsorbate such as the volcano curve of Fig. , the potential of dynamic operation is limited as shown in Fig. . There exist at least two cases where the slope of the volcano curve is horizontal on one side as drawn: