Dynamics of Site-Specific Ion Desorption Reactions

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We investigated site-selective chemical bond scission by core excitation for methyl-ester terminated self-assembled monolayer (SAM) in order to improve the selectivity and to elucidate the dynamics of this reaction, and obtained many important results as follows:(1) Primary bond scission occurs within ester group and its selectivity becomes much higher than PMMA. We have succeeded to evaluate direct and indirect processes quantitatively and obtained the selectivity is more than 90% for SAM and 60% for PMMA.(2) From polarization dependent experiments, it was found that ions which desorb selectively indicate significant polarization dependence, while non-selective ions rarely show the dependence. These findings indicate that initial memory of primary excitation is effectively conserved during reactions. From these results we proposed an active control of chemical bond scission just by changing an angle of incident radiation.(3) Selective bond scission of O-CH_3 could be achieved at both … More resonant excitations of o^*(O-CH_3)← C_<1s>(O-CH_3) and O_<1s>(O-CH_3). Distribution of CH_n^+ (n=1-3), however, is different at the position of primary excited atoms. At C excitation, Auger final energy is concentrated within removing CH_3+ and is effectively used for further fragmentation (named as "Hard-Cut"), but at O excitation, Auger energy easily diffuses into the substrate and not effectively used for the fragmentation (named as "Soft-Cut").(4) The dynamics of resonant core-excited states have been investigated theoretically by DFT theory and succeeded to find systematic relationship between chemical bond and potential gradient in the core-excited state, which plays an important role for the selective bond scission. Some general regularities were found: The gradient of core-excited state becomes more negative with increasing sum of the atomic numbers of bonding pair atoms, atomic number by core-excited atom, and the bond order. These rules are important to predict and design the site-selective bond scission reactions. Less