Fig. 6

Scaling of frequencies with adsorption energy. Frequencies are for the ν ⊥ mode and calculated from DFT for CH X species, where X ≥ 0. Included are modes and adsorption energies at atop sites (blue circles) and fcc hollow sites (green squares). Fits to Eq. (17) are shown by solid blue and dashed green lines, respectively. The slopes of the regressed lines are −192,000 and −63,100 for the blue and green lines, respectively. The intercepts are also both negative