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 (SI D) experiments is probed using infrared reflection absorption and scat tered 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 m odification consists of C-H and C-C bond cleavage in the hexanethiolat e adsorbate. Ion-induced adsorbate modification appears at an ion kine tic energy threshold of similar to 20 eV and rises sharply at 25 and 3 2 eV but is independent of the species of the incident ion. Even after extensive ion bombardment of the hexanethiolate, the scattered ion sp ectra observed during SID remain virtually unchanged. Collected from g as phase prepared self-assembled monolayers at atypically high ion exp osures of > 10(14) ions/cm(2), these results nonetheless indicate that SID spectra recorded under practical conditions (i.e., solution prepa red self-assembled monolayers and lower ion doses) should be stable an d reproducible.