Finally, we would like to note that there is a slow decay of the background level over the entire sequence (Figure ), which we assign to a slow pump-off of the gases created during the preceding catalyst reduction by CO/Ar pulsing. This was corrected for in the integration of the CO2 pulses. during the whole sequence, with sizes of 14.5% and 19.5% of the CO2 pulse intensity (Figure ), respectively, providing further support for our above assignment (section 3.1) that these signals arise from CO2 fragmentation.