Element-specific and site-specific ion desorption from adsorbed molecules by deep core-level photoexcitation at theK-edges

Abstract

This article reviews our recent work on the ion desorption from adsorbed and condensed molecules at low temperature following the core-level photoexcitations using synchrotron soft x-rays. The systems investigated here are adsorbed molecules with relatively heavy molecular weight, containing third-row elements such as Si, P, S, and Cl. Compared with molecules composed of second-row elements, the highly element-specific and site-specific fragment-ion desorptions are observed when we tune the photon energy at the dipole-allowed 1s→σ*(3p*) resonance. On the basis of the resonance Auger decay spectra around the 1s ionization thresholds, the observed highly specific ion desorption is interpreted in terms of the localization of the excited electrons (here called “spectator electrons”) in the antibonding σ* orbital. In order to separate the direct photo-induced process from the indirect processes triggered by the secondary electrons, the photon-stimulated ion desorption was also investigated in well-controlled mono- and multilayer molecules. The results confirmed that the resonant photoexcitation not in the substrate but in the thin films of adsorbates plays a significant role in the realization of the highly specific ion desorption.

Application of the equivalent‐core calculation to the Cl in core level on condensed SiCl4

“…This identification is consistent with the experimental spectrum of condensed SiCl 4 in Ref. [1]. Table II presents the thresholds for the various core excitations around the Cl K edge.…”

“…The higher desorption in the 8a 1 resonance indicates that the time scale of the SOCl bond scission and Cl ϩ desorption is comparable or faster than that of the delocalization of the excited states [1]. In the breaking process, if the delocalization of the excitation occurs before the chemical bond scission, the Auger electrons and succeeding secondary electron are the main trigger of the bond-breaking and ion desorption [1]. Figure 2 shows the desorption yields for the Cl ϩ ions around the Cl K edge excitation as a function of photon energy in the absorption spectrum (Fig.…”

“…The desorption is basically produced by Cl 1s 3 * (8a 1 ) excitation, because the spectator electron in 8a 1 is more effective for dissociation with the SiOCl bond than the spectator electron in 9t 2 . The higher desorption in the 8a 1 resonance indicates that the time scale of the SOCl bond scission and Cl ϩ desorption is comparable or faster than that of the delocalization of the excited states [1]. In the breaking process, if the delocalization of the excitation occurs before the chemical bond scission, the Auger electrons and succeeding secondary electron are the main trigger of the bond-breaking and ion desorption [1].…”

“…[1]. The study-selective bond breaking in the system using excitation was first carried out with thin films of PMMA (poly-methylmethacrylate) [17].…”

“…rocesses at solids surfaces have attracted considerable attention, not only as a fundamental science, but also as technological applications because they allow us to synthesize new materials [1]. Control of chemical reaction using electromagnetic radiation is one of the main issues of photochemistry, while one of the essential concepts of control is how selectively the chemical bond can be scissored [2].…”