Theoretical and Experimental Study of Soft X-ray Photoionization of Kr-Like Ions: 4s-Subshell Photoabsorption of Y 3+ P. Yeates 1 , E.T. Kennedy 1 , J-P. Mosnier 1 , P. van Kampen 1 , M.W.D. Mansfield 2 , J.Pedregosa-Gutierrez 3 , J. B. Greenwood 3 , Ph.V. Demekhin 4 , B.M.Lagutin 4 , V.L. Sukhorukov 4 , and J.T. Costello 1 1 National Centre for Plasma Science and Technology and School of Physical Sciences, Dublin City University, Dublin 9, Ireland 2 Department of Physics, University College Cork, Cork, Ireland 3 Atomic and Molecular Physics Div., Dept. of Pure and Applied Physics, Queens University Belfast, N. Ireland, UK 4 Rostov State University of TC, 344038 Rostov on Don, Russia E-mail: john.costello@dcu.ie As archetypal systems for the study of the atomic photoelectric effect, rare gas atoms, with their closed shell electronic configurations, have been the subject of innumerable experimental and theoretical investigations during the past four decades [1]. However, the situation for ions is far less complete due to the experimental difficulties and the concomitant paucity of measure- ments. Two techniques, one using a pair of synchronized laser plasmas (known as DLP) [2] and the other involving merged ion and synchrotron beams [3] are now routinely providing relative and absolute photoionization data on ions and so this situation is rapidly improving. Using the DLP technique we have already studied the 3s-subshell photoabsorption spectra of the Ar-like isoelectronic sequence [4] and more recently 4s-subshell exciataion in the Kr-like ions Rb + and Sr 2+ [5]. Due to experimental difficulties it was not previously possible for us to make convincing mea- surements of the Kr-like Y spectrum. However, with a new, more flexible target alignment/laser focusing optics arrangement in place we can now report here the extension of this latter work to the fourth member of the sequence Y 3+ using the DLP technique. The triply ionized yttrium ions were isolated in a laser produced plasma and their XUV absorption spectrum measured at DCU. The spectrum already compares well with a theoretical photoionization cross section computed within the framework of Configuration Interaction Pauli Fock Calculations. The cal- culations also predict that the first member of the Rydberg series (4s - 5p) drops below the 4p- threshold and that the q- values for the other series members become quite large in contrast to earlier isoelectronic sequence members [5]. References [1] V. Schmidt, Rep. Prog. Phys. 55, 1483 (1992), U.Becker, J Elec. Spec. 112, 47 (2000). [2] J. T. Costello, J-P. Mosnier, E. T. Kennedy, P. K. Carroll, and G. O’Sullivan, Phys.Scr. 34, 77 (1991). [3] A. Aguilar, J. B. West, R. A. Phaneuf, R. L. Brooks, F. Folkmann, H. Kjeldsen, J. D. Bozek, A. S. Schlachter, and C. Cisneros, Phys. Rev. A 67, Art. No. 012701 (2003). [4] P. van Kampen, G. O’Sullivan, V. K. Ivanov, A. N. Ipatov, J. T. Costello, and E. T. Kennedy, Phys. Rev. Lett. 78, 3082 (1997). [5] A. Neogi, E. T. Kennedy, J-P. Mosnier, P. van Kampen, G. O’Sullivan, M. W. D. Mansfield, Ph. V. Demekhin, B. M. Lagutin, I. D. Petrov, V. K. Sukhorukov, and J. T. Costello, (To appear in Phys. Rev. A June. 2003).