Photon-Stimulated Desorption due to Multielectron Excitations in Chemisorbed Molecules: CO on Ni(100)

Abstract

The ${\mathrm{O}}^{+}$ ion yield above the $\mathrm{O}(1s)$ absorption threshold ($K$ edge) from CO on Ni(100) is found to deviate significantly from the absorption coefficient. It exhibits a delayed onset by more than 20 eV with a broad maximum more than 100 eV above the threshold. This indicates the dominance of multielectron excitations over Auger deexcitation as the bond-breaking step for ${\mathrm{O}}^{+}$ desorption from chemisorbed CO molecules. Fine structure in the ${\mathrm{O}}^{+}$ yield around 50 eV above threshold is assigned to a resonant shake-off process.