J. Phys. IV France 7 (1997) C2-505-C2-506
Comparison between Electron Yield, PSD Ion Yield, and Surface Pipico Yield in Near C and O K-Edge XAFS in Condensed Methyl Formate-DT. Selriguehi1, H.L. Sekiguchi2, K. Obi3 and K. Tanaka4
1 department of Synchrotron Radiation Facility Project, Japan Atomic Energy Research Institute lamigohri, Hyogo 678-12, Japan
2 Electrotechnical Laboratory, 1-1-4 Umezono, Tsukuba305, Japan
3 Department of Chemistry, Tokyo Institute of Technology, Meguro, Tokyo 152, Japan
4 Department of Materials Science, Hiroshima University, Higashi-Hiroshima 724, Japan
We have studied the near edge X-ray absorption fine structure of photon stimulated desorption (PSD-NEXAFS) of positive ions from condensed layer of methyl formate-d (DCOOCH3) in the C K-edge (280-310 eV) and O K-edge (520- 560 eV). Ion yields of H+, D+ , CHn+ , O+, and OCHn+ , (n=0-3) can be concurrently taken as a function of photon energy, using a time-of-flight (TOF) spectroscopy with pulsed synchrotron radiation. We find that fragment ion yields show particular enhancement of the core resonance corresponding to certain antibonding states, compared with the photoabsorption cross section curve. We utilize a photoion pftotoion coincidence (PIPICO) technique for investigating the PSD pathways. The results give a good correlation between PIPICO yields and ion yields in the resonance. We conclude that the fragmentation pathway includes the formation step of multiple-charged precursor after the core resonant excitation even near edges, and that highly energetic fragments decomposed from such a precursor survive quenching or reneutralization by the surface and can desorb as ions.
© EDP Sciences 1997