ABSOLUTE PHOTOIONIZATION CROSS SECTION MEASUREMENTS OF Xe^+ IONS IN THE 4d-THRESHOLD ENERGY REGION A. Ito*, Y. Itoh&, M. Kitajima#, T. Koizumi*, T. M. Kojima$, H. Sakai*, M. Sano# and N. Watanabe+ * Department of Physics, Rikkyo University, Tokyo 171-8501, Japan & Physics Laboratory, Josai University, Saitama 350-0295, Japan # Department of Physics, Sophia University, Tokyo 102-8554, Japan $ The Institute of Physical and Chemical Research, Saitama 351-0198, Japan # Photon Factory, KEK, Ibaraki 305-0801, Japan + Institute of Low Temperature Science, Hokkaido University, Hokkaido 060-0819, Japan By using a photon-ion merged-beam apparatus, absolute photoionization cross sections for Xe^2+ and Xe^3+ production from the Xe^+ ions (4d^10 5s^2 5p^5 ^2P_3/2,1/2) were measured in the energy range from 80 eV to 140 eV. The energy dependence of the cross section for Xe^3+ production shows typical 4d "giant" resonance structure and the cross section has maximum value of 2.7 x 10^-17 cm^2 at about 100 eV. The cross section for Xe^2+ production does not show strong energy dependence; the maximum value is 3.4 x 10^-18 cm^2 at about 100 eV.