Isotope mixing between chemisorbed CO molecules on a K promoted Ni(111) surface: an LITD study

Abstract

The laser induced thermal desorption technique (LITD) is used to monitor the extent of isotope mixing between CO molecules on a potassium promoted, ( θ K = 0.28) Ni(111) surface. The onset of isotope mixing is found to occur at 400 K, well below the CO or potassium thermal desorption temperature. The maximum mixing yield is about 60% of the statistical limit over the temperature range of 450 to 600 K, suggesting that not all CO on the surface participates in the isotopic mixing reaction due to limited mobility. It is shown that the LITD technique can be used to measure the rate of mixing at temperatures well below that at which thermal desorption occurs. At 475 K the observed isotope exchange rate is consistent with a second order rate constant of k = 6 × 10 −2 ML −1 s −1.