$B!!!!!!!!!!(B4d PHOTOIONIZATION OF SINGLY CHARGED Cs+ ION T. Koizumi1, Y. Itoh2, A. Ito1, T. M. Kojima3, M. Sano4 and N. Watanabe5 1Department of Physics, Rikkyo University, Toshima-ku, Tokyo 171-8501, Japan 2Physics Laboratory, Josai University, Sakado, Saitama 350-0295, Japan 3The Institute of Physical and Chemical Research (RIKEN), 4Photon Factory, KEK, Tsukuba, Ibaragi 305-0801, Japan 5Institute of Low Temperature Science, Hokkaido University, Sapporo, Hokkaido 060-0819, Japan The relative photoion yield spectra of Cs2+ and Cs3+ from a Cs+ target within the 4d excitation region have been measured with an ion-photon merged-beam apparatus. A broad 4d giant resonance peak is observed clearly above 90 eV for Cs3+ spectrum. Below 90 eV, some prominent discrete peaks are observed. Tran- sition energies of these peaks agree very well with those of Cummings et al.