J. Phys. IV France 7 (1997) C2-499-C2-500
Surface and Bulk σ*(C-D) States in NEXAFS Spectra of Condensed Formic Acid LayersH.I. Sekiguchi1, T. Sekiguchi2 and K. Tanaka3
1 Ekctrotechnical Laboratory, 1-1-4 Umezono, Tsuhuba 305, Japan
2 Department of Synchrotron Radiation Facility Project, Japan Atomic Energy Research Institute, Mai 319-11, Japan
3 Department of Materials Science, Hiroshima University, Higashi-Hiroshima 724, Japan
C X-shell near edge X-ray absorption fine structure (NEXAFS) spectra of condensed layers of formic acid (DCOOD) have been recorded using the CKW Auger electron yield (AEY) and the photon-stimulated ion desorption (PSID) yield of D+ . It is found that the position of σ*(C-D) resonance in the AEY is much higher than that in the D+ PSID yield which is similar to that in the AEY of formic acid monolayer. This indicates that PS1D-NEXAFS is extremely surface sensitive while AEY-NEXAFS reflects a bulk state. The higher energy shift can be explained by the antibonding nature of σ*(C-D) excited state. The obtained results demonstrate that excitation of a strongly antibonding molecular orbital shifts to higher energy in the bulk compared with the surface by final-state interactions. These results have broad implications for the assignments of NEXAFS peaks in other systems.
© EDP Sciences 1997