Low-energy ion--surface reactions of pyrazine with two classes of self-assembled monolayers: influence of alkyl chain orientation.

Collisions of pyrazine with two classes of self-assembled monolayer (SAM) films are employed to determine whether surface confinement and the resulting alkyl chain orientation, influences low-energy ion-surface reactions. SAM films formed from n-alkanethiols (CH3(CH2)n-S-Au, n = 14-17) and 4-(4-alkoxyphenylbenzenethiols (4-(4-CH3(CH2)mOC6H4)-C6H4-S-Au, m = 14-17) chemisorbed onto Au (111) substrates are known to exhibit a chain-length-dependent odd-even effect that places the terminal C-C bond into different orientations. Ion-surface collisions (20 eV) of pyrazine molecular ion (M = m/z 80) with these surfaces yield reaction product ions corresponding to the addition of hydrogen atoms ([M + H]+ = m/z 81) and methyl groups ([M + CH3]+ = m/z 95) from the surface to the probe ion.