Configuration dependence of photon stimulated ion desorption from methyl ester compounds induced by core excitation

Photon stimulated ion desorption (PSID) from methyl ester terminated self-assembled monolayer (MHDA-SAM, HS(CH2)15COOCH3) and methyl mercaptoacetate (MA, HSCH2COOCH3) on Ag has been investigated using soft X-ray in the C and O K-edge regions. In MHDA-SAM on Ag, site-selective ion desorption has been clearly observed at resonant core excitations of C1s, O1s(OCH3) → σ∗(OCH3) and O1s(OCH3) → σ∗(COCH3). Ion intensity in MA on Ag is obviously reduced for CHn+ (n = 1-3) at C1s, O1s(OCH3) → σ∗(OCH3) excitations, and no site-selective reaction at O1s(OCH3) → σ∗(COCH3) excitations has been observed. These reactions may be influenced by configurational difference of reactive sites. It is suggested that surface effects on the selective reaction due to positioning methyl ester group near the surface plays an important role.