Selective chemical bond breaking characteristically induced by resonant core excitation ofester compounds on a surface

Abstract

Inner-shell excitation possesses an attractive potential to induce selective chemical bondbreaking due to its special localization and atomic selectivity. This paper reviews our recentworks about site-selective (or site-specific) photon stimulated desorption (PSD) ofcore-excited ester compounds, poly(methyl methacrylate) (PMMA) thin films, condensedmethyl isobutyrate (MIB) multilayers, methyl ester terminated self-assembled monolayers(SAMs), partially deuterided SAMs and ethyl ester terminated SAMs. Exact selective bondbreaking was observed for all molecular systems except for MIB multilayers: COO–R(R = CH3,C2H5) breaking in the , O 1s(OR) excitations and CO–OR in the excitation. Such resonant excitations take place within the functional group locally andthe initial memory of the excited site and its localization character is effectivelyconserved during the PSD process even after subsequent Auger decays and ionicdissociation/desorption. Variation of selectivity observed here indicates the importanceof the molecular environment and the contribution of the indirect dissociationprocess due to statistical energy relaxation and x-ray-induced electron stimulateddesorption. The obvious polarization dependence measured only for selectivelydesorbing ions also supports the above characteristics. Neutral fragments desorbingfrom core-excited PMMA follow the profile of the total electron yield spectrumbut not the partial ion yield of corresponding ions. This result indicates thationic dissociation locally promoted by Coulomb repulsion plays an important roleto reveal site-selectivity in chemical reactions induced by core-level excitation.