(a) Integrated area of CO TOF spectra as a function of desorption angle for a total exposure to ∼20 ML Ar. The intensities have been normalized to the intensity of the corresponding direct (Ar) beam. (b) Corresponding energy of the desorbing CO as a function of desorption angle. The line represents the elastic collision model of mass 29 being recoiled by mass 40.
(a) Time series of TOF spectra tracking CO desorption along θ d = 0°. The distributions are collected sequentially from the bottom to the top. They are plotted on the same scale, but are offset for clarify. The total exposure is ∼20 ML of Ar. Each individual distribution corresponds to an Ar exposure of ∼2.8 ML. (b) Plot of the integrated areas determined from raw TOF spectra at #3 and #7 in time series measured as a function of θ d. (c) The cumulative TOF spectrum arising from the average of the seven spectra shown in panel (a). The line through the data points is the result of fitting with a single shifted Maxwell–Boltzmann distribution as described in the text.
Time series of TOF spectra tracking Ar scattering along θ f = 15°, 45°, and 75°. The distributions are collected sequentially from the bottom to the top, with each individual distribution corresponding to an Ar exposure of ∼2.8 ML. The curves within individual panels are plotted on the same scale, but offset for clarity. The uppermost curve on each panel is the average distribution derived from the seven lower spectra. The lines through the data points are the net result of fitting with single (θ f = 15°) and double (θ f = 45°; 75°) shifted Maxwell–Boltzmann distributions.
(a) Normalized total integrated area of the TOF spectra as a function of θ f for TOF series #1 and #7. The inset is an expanded view of the region for θ f = 0–50°. (b) The average energies of the fast (open circles) and slow (filled circles) components as a function of θ f derived from the cumulative Ar TOF spectra. Three elastic binary collision models are reproduced on this panel. From the top these are: Ar (mass 40) scattered by Ru (mass 101); by 2×13CO (mass 58); and by 13CO (mass 29). The inset shows the corresponding normalized intensities of the two components derived from the cumulative TOF spectra.
Comparison of TOF spectra from bare (red), partially CO-covered (blue), and CO-saturated (green) Ru(0001) surfaces for spectra measured at θ f = 30°, 60°, and 75°. The spectra at θ f = 30° have been offset for clarity. The spectra from the CO-saturated surface (TOF #1) were collected during Ar exposure of ∼0–3 ML; those from the partially CO-covered surface (TOF #7) were collected during Ar exposure of ∼17–20 ML. The intensities have been adjusted on the basis of a normalized direct beam intensity.
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