MOLECULAR ION MODIFICATION OF A HEXANETHIOLATE SELF-ASSEMBLED MONOLAYER DURING SURFACE-INDUCED DISSOCIATION

The modification of a hexanethiolate self-assembled monolayer (CH3(CH2)(5)S) adsorbed on Ag (111) by exposure to pyridine, thiophene, furan, and tert-butyl molecular ions during surface-induced dissociation (SID) experiments is probed using infrared reflection absorption and scattered ion spectra. As much as 60% of the monolayer is modified after a 2.9 X 10(14) ions/cm(2) exposure at an energy of 32 eV. Ion-induced modification consists of C-H and C-C bond cleavage in the hexanethiolate adsorbate. Ion-induced adsorbate modification appears at an ion kinetic energy threshold of similar to 20 eV and rises sharply at 25 and 32 eV but is independent of the species of the incident ion. Even after extensive ion bombardment of the hexanethiolate, the scattered ion spectra observed during SID remain virtually unchanged. Collected from gas phase prepared self-assembled monolayers at atypically high ion exposures of > 10(14) ions/cm(2), these results nonetheless indicate that SID spectra recorded under practical conditions (i.e., solution prepared self-assembled monolayers and lower ion doses) should be stable and reproducible.