Isotope effect in electron stimulated desorption: The role of internal degrees of freedom in CO desorption from Pt(111)

Abstract

Width of particle beams desorbed in electron stimulated desorption: O+ and metastable CO from CO/Pt(111) J. Chem. Phys. 98, 689 (1993); 10.1063/1.464614Rotational dynamics and electronic energy partitioning in the electronstimulated desorption of NO from Pt (111) Electron stimulated desorption ͑ESD͒ of CO ϩ , O ϩ , metastable neutral CO*, and ground state neutral CO from the CO/Pt͑111͒ was studied, using isotopic substitution of CO. Four isotopic versions of CO were compared in their desorption behavior. Contrary to the prediction of theoretical models that suggest a decrease of the ESD yield with increasing mass of a given desorption product, the CO ϩ and CO* ESD yields were found to be larger from the ͑heavier͒ 12 C 18 O than from the ͑lighter͒ 13 C 16 O adsorbate. The O ϩ ESD yields followed the expected trend Y ͑ 16 O ϩ ͒ϾY ͑ 18 O ϩ ͒. No isotope effect was observed for ground state neutral CO desorption. Qualitative arguments explaining the anomalous isotope effect, and emphasizing the importance of internal dynamics, in particular, the rotation of diatomic desorption products in the ESD process, are presented. Here it is shown that the velocity of departure of the carbon end of the rotating CO molecule may control neutralization or quenching effects for CO ϩ or CO* produced by electron stimulated desorption. Thus, neutralization or quenching of the excited CO species occurs via carbon-centered orbitals of the departing species.

Photochemistry at nanoparticulate surfaces

“…No laser activity is observed when irradiating a normal coverage of CO adsorbed via background dosing palladium particles. In contrast to CO/Pt ESDIAD studies [79], the lack of desorption of neutral, electronically excited CO may be explained by preferential CO bonding to hollow sites on Pd while CO prefers terminal bonding on Pt. In a hollow site position CO experiences a higher quenching probability and a lower cross section for initial excitation due to a larger amount of metal-electron backdonation in contrast to terminal or bridging CO.…”