CORE EXCITATION-INDUCED PHOTODESORPTION OF MOLECULAR AND FRAGMENT IONS FROM NO ON RU(001)

Using synchrotron light, the desorption of NO+, O+ and O2+ from molecular NO adsorbed on Ru(001) has been investigated in the core excitation region, i.e., at and above the N 1s and O 1s thresholds. The most abundant ion is O+ which shows multiple, polarization dependent structure above O 1s indicating that core shake-up and shake-off excitations lead to particularly high yields, as has been found previously for adsorbed CO. The yields of NO+ are much smaller, and are more closely related to the total core excitation cross sections at both N 1s and O 1s. The O+ signal at N 1s may behave similarly but cannot be investigated in detail due to its small cross section and high background. Liberation of O2+ is found for even higher excitations above O 1s than O+. No N+ could be detected. The energy and polarization dependent data are used for assignments of desorption mechanisms and related excitations and decay sequences. As for adsorbed CO, strongly correlated complex primary and secondary electronic states are found to lead to the highest desorption yields, which is attributed to their particularly strong localization. Also, as for adsorbed CO, contributions of incipient bond breaking during core hole lifetimes appear probable. Temperature and coverage dependent measurements and comparison with UPS data allow a correlation to the various surface species known from earlier work to exist in this adsorption system; the linearly bound v2-state is found to be the main source of photodesorption.