Data analysis. (a) XPS C1s and (b) XPS Au 4f data for CO adsorbed on gold at 10 K, at 0.0 ML and 0.8 ML of CO exposure. (c) Number of CO layers deposited on gold as a function of CO exposure, deduced from the infrared strength of the stretching CO band at 2142 cm⁻¹. IR intensities follow the diagonal line when SC=1. (d) C1s XPS data for CO adsorbed on soot at 10 K, at 0.0 ML and 12.5 ML of CO exposure. (e) CO coverage per unit surface area (in percent) deduced from the XPS signals (see the main text) as function of the CO exposure. The graphical method for determining the SC of CO on soot consists in dividing the exposure on gold (point 2) by the exposure on soot (point 3) necessary to obtain the same coverage (point 1; see the main text).