FRAGMENTAION OF ACETONE FOLLOWING SELECTIVE INNER-SHELL EXCITATION USING SR SOFT X-RAYS Isao H. Suzuki and Norio Saito Electrotechnical Laboratory, Tsukuba, Ibaraki, 305-8568 Japan Fragment ions from acetone have been measured in the soft X-ray region using monochromatized synchrotron radiation and a time-of-flight mass spectrometer. In comparison among p* excitation, Rydberg orbital excitation and ionization near the CK-edges, the ionization induces a steeper decomposition than the others, e.g. relative intensities of CnH+ become higher than CnH2+ and CnH3+. Significant site-specific decomposition was not found in the CK-edges and the OK-edge.