PYRIDINE ION COLLISIONS WITH PYRIDINE-D(5) MULTILAYERS ON AG(111) - NEW SCATTERED IONS AND NEUTRALIZATION QUENCHING

Surface-induced dissociation (SID) is examined for 32-eV pyridine-h5 i ons incident on pyridine-d5 multilayers adsorbed on Ag(111). The total scattered ion signal increases by a factor of 50 as the pyridine-d5 c overage increases from 1.3 to 3 ML and then remains constant from 3 to 6 ML. The scattered ion signal enhancement varies from a factor of 10 to 50 for individual ions. Both pyridine molecular ions (C5H5N+) and sputtered adsorbate (C5D5N+) are observed in the scattered ion spectra off the multilayer whereas they are absent off the monolayer and subm onolayer. The changes in the SID fragmentation pattern can be explaine d by the emergence of three new ions: C5H5N+, CsH4N+, and C5D5N+. The signal enhancement with adsorbate coverage is explained by a neutraliz ation quenching model where the adsorbate behaves as a spacer layer wh ich increases the closest ion-surface distance and thus reduces the ch arge-transfer probability.